目录

通过Kurento API创建客户端应用程序

Kurento 是什么?

Kurento 是一个 WebRTC 媒体服务器和一组客户端API，为 WWW 和智能手机平台开发高级视频应用程序。 Kurento 的特点包括群组通信、转码、录音、混合、广播和音频流的路由。

Kurento 还提供先进的媒体处理能力，包括计算机视觉、视频索引、增强现实和语音分析。 Kurento 模块化架构简化了第三方媒体处理算法（例如：语音识别、情感分析、人脸识别等）的集成，应用程序开发人员可以透明地使用它作为 Kurento 内置功能的其余部分。

Kurento 的核心元素是 Kurento Media Server （Kurento媒体服务器）, 负责媒体的传播、处理、加载和记录。在基于 GStreamer 的底层技术中实现资源消耗优化。 它提供了以下功能:

  • 网络流协议，包括 HTTP, RTP 和 WebRTC。
  • 群组通信(MCUs和SFUs功能)支持媒体混合和媒体路由/分发。
  • 对计算视觉和增强现实过滤器的一般支持。
  • 媒体存储支持 WebM 和 MP4 的写入操作，并使用 GStreamer 支持的所有格式进行播放。
  • 在 GStreamer 支持的任何编解码器之间自动媒体转换，包括 VP8、H.264、H.263、AMR、OPUS、Speex、G.711 等格式。

在 Java 和 Javascript 中有可用的 Kurento Client 库，可以从应用程序中控制 Kurento媒体服务器。如果您喜欢其他的编程语言，则可以使用基于 WebSocket 和 JSON-RPC 的 Kurento Protocol。

Kurento是开源的，根据 Apache 2.0 许可协议发布。它的源代码托管在 GitHub 上。

如果您想快速上手，最好的方法是 安装Kurento媒体服务器，并以运行演示应用程序的形式查看我们的 教程。您可以选择您喜欢的技术来构建多媒体应用程序: Java、浏览器 JavaScript 或 Node.js。

如果您想充分使用 Kurento，请参考 高级文档。

Kurento 简介

WebRTC 媒体服务器

WebRTC 是一种开放源码技术，可以通过 JavaScript APIs 使web浏览器具有实时通信(Real-Time Communications, RTC)功能。它被认为是一种点对点技术，在这种技术中，浏览器可以直接通信，而不需要任何基础设施中介。这个模型足以创建基本的应用程序，但在它上面很难实现像组通信、媒体流录制、媒体广播或媒体转换等功能。出于这个原因，许多应用程序需要使用媒体服务器。

Peer-to-peer WebRTC approach vs. WebRTC through a media server

点对点WebRTC方法 vs. WebRTC通过媒体服务器

从概念上讲，WebRTC媒体服务器只是一种“多媒体中间件”（它位于通信节点的中间），媒体流量通过它从源移动到目的地。媒体服务器能够处理媒体流和提供不同类型包括组通信(分发媒体流从一个生产者到多个接收器，例如充当Multi-Conference Unit, MCU)、混合(将几个输入流转换为一个复合流)、转码(在不兼容的客户端之间适配编解码器和格式)、记录(节点间交换的媒体进行持久化存储)等等。

Typical WebRTC Media Server capabilities

典型的WebRTC媒体服务器功能

Kurento 媒体服务器

在Kurento架构的核心是一个名为 Kurento Media Server (KMS) 的媒体服务器。Kurento媒体服务器基于可插入的媒体处理功能，这意味着它所提供的任何功能都是可以被激活或停用的可插入模块。此外，开发人员可以无缝地创建额外的模块，可以动态扩展Kurento媒体服务器的新功能。

Kurento媒体服务器提供开箱即用的组通信、混合、转码、录音和播放功能。此外，它还为媒体处理提供了高级模块，包括计算机视觉、增强现实、alpha混合等。

Kurento Media Server capabilities

Kurento媒体服务器功能

Kurento API、客户端和协议

Kurento媒体服务器的功能由 Kurento API 公开给应用程序开发者。这个API是通过称为 Kurento Clients 的库实现的。Kurento为 Java 和 JavaScript 提供了两个客户端。如果你喜欢其他语言，你仍然可以直接使用 Kurento协议。该协议允许控制Kurento媒体服务器，它基于互联网标准，如 WebSocket 和 JSON-RPC。下图显示了如何在三种情况下使用Kurento客户端：

  • 直接在兼容 WebRTC 的浏览器中使用Kurento JavaScript客户端
  • 在Java EE应用服务器中使用Kurento Java客户端
  • 在Node.js服务器中使用Kurento JavaScript客户端
Connection of Kurento Clients (Java and JavaScript) to Kuento Media Server

将Kurento客户端（Java和JavaScript）连接到Kuento媒体服务器

这三种技术的完整示例在 教程 部分中有描述。

Kurento客户端的API基于 Media Element 的概念。媒体元素拥有特定的媒体功能。例如，称为 WebRtcEndpoint 的媒体元素具有发送和接收WebRTC媒体流的能力，称为 RecorderEndpoint 的媒体元素具有将其接收的任何媒体流录入文件系统的能力，FaceOverlayFilter 会检测交换的视频流上的人脸，并添加一个特定的覆盖图像在其上，等等。Kurento公开了一个丰富的媒体元素工具箱作为其API的一部分。

Some Media Elements provided out of the box by Kurento

Kurento提供的一些媒体元素

为了更好地理解这些概念，建议您查看 Kurento API 和 Kurento Protocol 部分。您还可以查看JavaDoc和JsDoc：

使用Kurento创建应用程序

从应用程序开发人员的角度来看，Media Elements 就像 Lego 一样：您只需要使用应用程序所需的元素，并按照所需的拓扑结构连接它们。在 Kurento 术语中，连接的媒体元素的图形称为 媒体管道(Media Pipeline)。 因此，在创建管道时，开发人员需要确定他们想要使用的功能（媒体元素）和拓扑结构，来确定哪些媒体元素向另外一些媒体元素提供媒体（连接性）。连接性是通过 connect 原语进行控制，暴露在所有 Kurento 客户端API 上。 这个原语总是在作为源的元素中调用，汇点元素作为下面模式的参数：

sourceMediaElement.connect(sinkMediaElement)

例如：如果要创建将 WebRTC流 录入文件系统的应用程序，则需要两个媒体元素： WebRtcEndpoint 和 RecorderEndpoint。 当客户端连接到应用程序时，您将需要实例化这些媒体元素，使得 WebRtcEndpoint （能够接收WebRTC流）接收到的流被馈送到 RecorderEndpoint （能够将媒体流记录到文件系统中）。 最后，您需要连接它们，以便前者接收到的流进入后者：

WebRtcEndpoint.connect(RecorderEndpoint)

为了简化WebRTC流在客户端的处理，Kurento 提供了一个名为 WebRtcPeer 的实用程序。 然而，标准的WebRTC API（getUserMedia 、 RTCPeerConnection 等）也可以用于连接到 WebRtcEndpoints。有关更多信息，请访问 教程 部分。

Simple Example of a Media Pipeline

媒体管道的简单示例

Kurento 媒体服务器安装

Kurento Media Server (KMS) has to be installed on Ubuntu 14.04 LTS (64 bits).

In order to install the latest stable Kurento Media Server version (6.6.1) you have to type the following commands, one at a time and in the same order as listed here. When asked for any kind of confirmation, reply affirmatively:

echo "deb http://ubuntu.kurento.org trusty kms6" | sudo tee /etc/apt/sources.list.d/kurento.list
wget -O - http://ubuntu.kurento.org/kurento.gpg.key | sudo apt-key add -
sudo apt-get update
sudo apt-get install kurento-media-server-6.0

Now, Kurento Media Server has been installed. Use the following commands to start and stop it respectively:

sudo service kurento-media-server-6.0 start
sudo service kurento-media-server-6.0 stop

Migrating from KMS v5 to v6

The current stable version of Kurento Media Server uses the Trickle ICE protocol for WebRTC connections. Trickle ICE is the name given to the extension to the Interactive Connectivity Establishment (ICE) protocol that allows ICE agents (in this case Kurento Media Server and Kurento Client) to send and receive candidates incrementally rather than exchanging complete lists. In short, Trickle ICE allows to begin WebRTC connectivity much more faster.

This feature makes the Kurento Media Server 6 incompatible with the former versions. If you are using Kurento Media Server 5.1 or lower, it is strongly recommended to upgrade your KMS. To do that, first you need to uninstall KMS as follows:

sudo apt-get remove kurento-media-server
sudo apt-get purge kurento-media-server
sudo apt-get autoremove

Finally, the references to the Kurento Media Server in the APT sources should be removed:

# Delete any file in /etc/apt/sources.list.d folder related to kurento
sudo rm /etc/apt/sources.list.d/kurento*

# Edit sources.list and remove references to kurento
sudo vi /etc/apt/sources.list

After that, install Kurento Media Server 6 as depicted at the top of this page.

STUN and TURN servers

If Kurento Media Server is located behind a NAT you need to use a STUN or TURN in order to achieve NAT traversal. In most of cases, a STUN server will do the trick. A TURN server is only necessary when the NAT is symmetric.

In order to setup a STUN server you should uncomment the following lines in the Kurento Media Server configuration file located on at /etc/kurento/modules/kurento/WebRtcEndpoint.conf.ini:

stunServerAddress=<stun_ip_address>
stunServerPort=<stun_port>

注解

Be careful since comments inline (with ;) are not allowed for parameter such as stunServerAddress. Thus, the following configuration is not correct:

stunServerAddress=<stun_ip_address> ; Only IP address are supported

... and must be:

stunServerAddress=<stun_ip_address>

The parameter stunServerAddress should be an IP address (not domain name). There is plenty of public STUN servers available, for example:

173.194.66.127:19302
173.194.71.127:19302
74.125.200.127:19302
74.125.204.127:19302
173.194.72.127:19302
74.125.23.127:3478
77.72.174.163:3478
77.72.174.165:3478
77.72.174.167:3478
77.72.174.161:3478
208.97.25.20:3478
62.71.2.168:3478
212.227.67.194:3478
212.227.67.195:3478
107.23.150.92:3478
77.72.169.155:3478
77.72.169.156:3478
77.72.169.164:3478
77.72.169.166:3478
77.72.174.162:3478
77.72.174.164:3478
77.72.174.166:3478
77.72.174.160:3478
54.172.47.69:3478

In order to setup a TURN server you should uncomment the following lines in the Kurento Media Server configuration file located on at /etc/kurento/modules/kurento/WebRtcEndpoint.conf.ini:

turnURL=user:password@address:port;

As before, TURN address should be an IP address (not domain name). See some examples of TURN configuration below:

turnURL=kurento:kurento@193.147.51.36:3478;

... or using a free access numb STUN/TURN server as follows:

turnURL=user:password@66.228.45.110:3478;

An open source implementation of a TURN server is coturn. In the FAQ section there is description about how to install a coturn server.

Kurento 教程

This section contains tutorials showing how to use Kurento framework to build different types of WebRTC and multimedia applications. Tutorials come in three flavors:

  • Java: These show applications where clients interact with Spring-Boot based application, that host the logic orchestrating the communication among clients and controlling Kurento Media Server capabilities.
  • Browser JavaScript: These show applications executing at the browser and communicating directly with the Kurento Media Server. In these tutorial all logic is directly hosted by browser. Hence, no application server is necessary.
  • Node.js: These show applications where clients interact with an application server based on Node.js technology. The application server holds the logic orchestrating the communication among the clients and controlling Kurento Media Server capabilities for them.

注解

The tutorials have been created with learning objectives. They are not intended to be used in production environments where different unmanaged error conditions may emerge. Use at your own risk!

注解

These tutorials require https in order to use WebRTC. Following instructions will provided further information about how to enable application security.

Hello world

This is one of the simplest WebRTC applications you can create with Kurento. It implements a WebRTC loopback (a WebRTC media stream going from client to Kurento and back to the client)

Java - Hello world

This web application has been designed to introduce the principles of programming with Kurento for Java developers. It consists on a WebRTC video communication in mirror (loopback). This tutorial assumes you have basic knowledge of JavaScript, HTML and WebRTC. We also recommend reading the Introducing Kurento section before starting this tutorial.

注解

This tutorial has been configured to use https. Follow the instructions to secure your application.

For the impatient: running this example

You need to have installed the Kurento Media Server before running this example. Read the installation guide for further information.

To launch the application, you need to clone the GitHub project where this demo is hosted, and then run the main class:

git clone https://github.com/Kurento/kurento-tutorial-java.git
cd kurento-tutorial-java/kurento-hello-world
git checkout 6.6.2
mvn compile exec:java

Access the application connecting to the URL https://localhost:8443/ in a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the flag kms.url to the JVM executing the demo. As we’ll be using maven, you should execute the following command

mvn compile exec:java -Dkms.url=ws://kms_host:kms_port/kurento
Understanding this example

Kurento provides developers a Kurento Java Client to control the Kurento Media Server. This client library can be used in any kind of Java application: Server Side Web, Desktop, Android, etc. It is compatible with any framework like Java EE, Spring, Play, Vert.x, Swing and JavaFX.

This hello world demo is one of the simplest web applications you can create with Kurento. The following picture shows a screenshot of this demo running:

Kurento Hello World Screenshot: WebRTC in loopback

Kurento Hello World Screenshot: WebRTC in loopback

The interface of the application (an HTML web page) is composed by two HTML5 video tags: one showing the local stream (as captured by the device webcam) and the other showing the remote stream sent by the media server back to the client.

The logic of the application is quite simple: the local stream is sent to the Kurento Media Server, which sends it back to the client without modifications. To implement this behavior, we need to create a Media Pipeline composed by a single Media Element, i.e. a WebRtcEndpoint, which holds the capability of exchanging full-duplex (bidirectional) WebRTC media flows. This media element is connected to itself so that the media it receives (from browser) is sent back (to browser). This media pipeline is illustrated in the following picture:

Kurento Hello World Media Pipeline in context

Kurento Hello World Media Pipeline in context

This is a web application, and therefore it follows a client-server architecture. At the client-side, the logic is implemented in JavaScript. At the server-side, we use a Spring-Boot based server application consuming the Kurento Java Client API, to control Kurento Media Server capabilities. All in all, the high level architecture of this demo is three-tier. To communicate these entities, two WebSockets are used. First, a WebSocket is created between client and application server to implement a custom signaling protocol. Second, another WebSocket is used to perform the communication between the Kurento Java Client and the Kurento Media Server. This communication takes place using the Kurento Protocol. For further information on it, please see this page of the documentation.

The diagram below shows a complete sequence diagram, of the interactions with the application interface to: i) JavaScript logic; ii) Application server logic (which uses the Kurento Java Client); iii) Kurento Media Server.

Complete sequence diagram of Kurento Hello World (WebRTC in loopbak) demo

Complete sequence diagram of Kurento Hello World (WebRTC in loopbak) demo

The following sections analyze in depth the server (Java) and client-side (JavaScript) code of this application. The complete source code can be found in GitHub.

Application Server Logic

This demo has been developed using Java in the server-side, based on the Spring Boot framework, which embeds a Tomcat web server within the generated maven artifact, and thus simplifies the development and deployment process.

注解

You can use whatever Java server side technology you prefer to build web applications with Kurento. For example, a pure Java EE application, SIP Servlets, Play, Vert.x, etc. Here we chose Spring Boot for convenience.

In the following, figure you can see a class diagram of the server side code:

Server-side class diagram of the HelloWorld app

Server-side class diagram of the HelloWorld app

The main class of this demo is HelloWorldApp. As you can see, the KurentoClient is instantiated in this class as a Spring Bean. This bean is used to create Kurento Media Pipelines, which are used to add media capabilities to the application. In this instantiation we see that we need to specify to the client library the location of the Kurento Media Server. In this example, we assume it is located at localhost, listening in port 8888. If you reproduce this example, you’ll need to insert the specific location of your Kurento Media Server instance there.

Once the Kurento Client has been instantiated, you are ready for communicating with Kurento Media Server and controlling its multimedia capabilities.

@EnableWebSocket
@SpringBootApplication
public class HelloWorldApp implements WebSocketConfigurer {

   @Bean
   public HelloWorldHandler handler() {
      return new HelloWorldHandler();
   }

   @Bean
   public KurentoClient kurentoClient() {
      return KurentoClient.create();
   }

   @Override
   public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
      registry.addHandler(handler(), "/helloworld");
   }

   public static void main(String[] args) throws Exception {
      new SpringApplication(HelloWorldApp.class).run(args);
   }
}

This web application follows a Single Page Application architecture (SPA), and uses a WebSocket to communicate client with application server by means of requests and responses. Specifically, the main app class implements the interface WebSocketConfigurer to register a WebSocketHanlder to process WebSocket requests in the path /helloworld.

HelloWorldHandler class implements TextWebSocketHandler to handle text WebSocket requests. The central piece of this class is the method handleTextMessage. This method implements the actions for requests, returning responses through the WebSocket. In other words, it implements the server part of the signaling protocol depicted in the previous sequence diagram.

public class HelloWorldHandler extends TextWebSocketHandler {

   private final Logger log = LoggerFactory.getLogger(HelloWorldHandler.class);
   private static final Gson gson = new GsonBuilder().create();

   @Autowired
   private KurentoClient kurento;

   private final ConcurrentHashMap<String, UserSession> users = new ConcurrentHashMap<String, UserSession>();

   @Override
   public void handleTextMessage(WebSocketSession session, TextMessage message) throws Exception {
      JsonObject jsonMessage = gson.fromJson(message.getPayload(), JsonObject.class);

      log.debug("Incoming message: {}", jsonMessage);

      switch (jsonMessage.get("id").getAsString()) {
      case "start":
         start(session, jsonMessage);
         break;
      case "stop": {
         UserSession user = users.remove(session.getId());
         if (user != null) {
            user.release();
         }
         break;
      }
      case "onIceCandidate": {
         JsonObject jsonCandidate = jsonMessage.get("candidate").getAsJsonObject();

         UserSession user = users.get(session.getId());
         if (user != null) {
            IceCandidate candidate = new IceCandidate(jsonCandidate.get("candidate").getAsString(),
                  jsonCandidate.get("sdpMid").getAsString(), jsonCandidate.get("sdpMLineIndex").getAsInt());
            user.addCandidate(candidate);
         }
         break;
      }
      default:
         sendError(session, "Invalid message with id " + jsonMessage.get("id").getAsString());
         break;
      }
   }

   private void start(final WebSocketSession session, JsonObject jsonMessage) {
      try {
         // 1. Media logic (webRtcEndpoint in loopback)
         MediaPipeline pipeline = kurento.createMediaPipeline();
         WebRtcEndpoint webRtcEndpoint = new WebRtcEndpoint.Builder(pipeline).build();
         webRtcEndpoint.connect(webRtcEndpoint);

         // 2. Store user session
         UserSession user = new UserSession();
         user.setMediaPipeline(pipeline);
         user.setWebRtcEndpoint(webRtcEndpoint);
         users.put(session.getId(), user);

         // 3. SDP negotiation
         String sdpOffer = jsonMessage.get("sdpOffer").getAsString();
         String sdpAnswer = webRtcEndpoint.processOffer(sdpOffer);

         JsonObject response = new JsonObject();
         response.addProperty("id", "startResponse");
         response.addProperty("sdpAnswer", sdpAnswer);

         synchronized (session) {
            session.sendMessage(new TextMessage(response.toString()));
         }

         // 4. Gather ICE candidates
         webRtcEndpoint.addIceCandidateFoundListener(new EventListener<IceCandidateFoundEvent>() {
            @Override
            public void onEvent(IceCandidateFoundEvent event) {
               JsonObject response = new JsonObject();
               response.addProperty("id", "iceCandidate");
               response.add("candidate", JsonUtils.toJsonObject(event.getCandidate()));
               try {
                  synchronized (session) {
                     session.sendMessage(new TextMessage(response.toString()));
                  }
               } catch (IOException e) {
                  log.error(e.getMessage());
               }
            }
         });
         webRtcEndpoint.gatherCandidates();

      } catch (Throwable t) {
         sendError(session, t.getMessage());
      }
   }

   private void sendError(WebSocketSession session, String message) {
      try {
         JsonObject response = new JsonObject();
         response.addProperty("id", "error");
         response.addProperty("message", message);
         session.sendMessage(new TextMessage(response.toString()));
      } catch (IOException e) {
         log.error("Exception sending message", e);
      }
   }
}

The start method performs the following actions:

  1. Configure media processing logic: This is the part in which the application configures how Kurento has to process the media. In other words, the media pipeline is created here. To that aim, the object KurentoClient is used to create a MediaPipeline object. Using it, the media elements we need are created and connected. In this case, we only instantiate one WebRtcEndpoint for receiving the WebRTC stream and sending it back to the client.
  2. Store user session: In order to release the resources in the Kurento Media Server, we store the user session (i.e. Media Pipeline and WebRtcEndpoint) to be able to perform a release process when the stop method is called.
  3. WebRTC SDP negotiation: In WebRTC, SDP (Session Description protocol) is used for negotiating media exchanges between peers. Such negotiation is based on the SDP offer and answer exchange mechanism. This negotiation is finished in the third part of the method processRequest, using the SDP offer obtained from the browser client and returning a SDP answer generated by WebRtcEndpoint.
  4. Gather ICE candidates: As of version 6, Kurento fully supports the Trickle ICE protocol. For that reason, WebRtcEndpoint can receive ICE candidates asynchronously. To handle this, each WebRtcEndpoint offers a listener (addOnIceGatheringDoneListener) that receives an event when the ICE gathering process is done.
Client-Side Logic

Let’s move now to the client-side of the application. To call the previously created WebSocket service in the server-side, we use the JavaScript class WebSocket. We use a specific Kurento JavaScript library called kurento-utils.js to simplify the WebRTC interaction with the server. This library depends on adapter.js, which is a JavaScript WebRTC utility maintained by Google that abstracts away browser differences. Finally jquery.js is also needed in this application.

These libraries are linked in the index.html web page, and are used in the index.js. In the following snippet we can see the creation of the WebSocket (variable ws) in the path /helloworld. Then, the onmessage listener of the WebSocket is used to implement the JSON signaling protocol in the client-side. Notice that there are three incoming messages to client: startResponse, error, and iceCandidate. Convenient actions are taken to implement each step in the communication. For example, in functions start the function WebRtcPeer.WebRtcPeerSendrecv of kurento-utils.js is used to start a WebRTC communication.

var ws = new WebSocket('ws://' + location.host + '/helloworld');

ws.onmessage = function(message) {
   var parsedMessage = JSON.parse(message.data);
   console.info('Received message: ' + message.data);

   switch (parsedMessage.id) {
   case 'startResponse':
      startResponse(parsedMessage);
      break;
   case 'error':
      if (state == I_AM_STARTING) {
         setState(I_CAN_START);
      }
      onError('Error message from server: ' + parsedMessage.message);
      break;
   case 'iceCandidate':
      webRtcPeer.addIceCandidate(parsedMessage.candidate, function(error) {
         if (error)
            return console.error('Error adding candidate: ' + error);
      });
      break;
   default:
      if (state == I_AM_STARTING) {
         setState(I_CAN_START);
      }
      onError('Unrecognized message', parsedMessage);
   }
}

function start() {
   console.log('Starting video call ...');

   // Disable start button
   setState(I_AM_STARTING);
   showSpinner(videoInput, videoOutput);

   console.log('Creating WebRtcPeer and generating local sdp offer ...');

   var options = {
      localVideo : videoInput,
      remoteVideo : videoOutput,
      onicecandidate : onIceCandidate
   }
   webRtcPeer = new kurentoUtils.WebRtcPeer.WebRtcPeerSendrecv(options,
         function(error) {
            if (error)
               return console.error(error);
            webRtcPeer.generateOffer(onOffer);
         });
}

function onOffer(error, offerSdp) {
   if (error)
      return console.error('Error generating the offer');
   console.info('Invoking SDP offer callback function ' + location.host);
   var message = {
      id : 'start',
      sdpOffer : offerSdp
   }
   sendMessage(message);
}

function onIceCandidate(candidate) {
   console.log('Local candidate' + JSON.stringify(candidate));

   var message = {
      id : 'onIceCandidate',
      candidate : candidate
   };
   sendMessage(message);
}

function startResponse(message) {
   setState(I_CAN_STOP);
   console.log('SDP answer received from server. Processing ...');

   webRtcPeer.processAnswer(message.sdpAnswer, function(error) {
      if (error)
         return console.error(error);
   });
}

function stop() {
   console.log('Stopping video call ...');
   setState(I_CAN_START);
   if (webRtcPeer) {
      webRtcPeer.dispose();
      webRtcPeer = null;

      var message = {
         id : 'stop'
      }
      sendMessage(message);
   }
   hideSpinner(videoInput, videoOutput);
}

function sendMessage(message) {
   var jsonMessage = JSON.stringify(message);
   console.log('Senging message: ' + jsonMessage);
   ws.send(jsonMessage);
}
Dependencies

This Java Spring application is implemented using Maven. The relevant part of the pom.xml is where Kurento dependencies are declared. As the following snippet shows, we need two dependencies: the Kurento Client Java dependency (kurento-client) and the JavaScript Kurento utility library (kurento-utils) for the client-side. Other client libraries are managed with webjars:

<dependencies>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-client</artifactId>
   </dependency>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-utils-js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars</groupId>
      <artifactId>webjars-locator</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>bootstrap</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>demo-console</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>adapter.js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>jquery</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>ekko-lightbox</artifactId>
   </dependency>
</dependencies>

注解

We are in active development. You can find the latest version of Kurento Java Client at Maven Central.

Kurento Java Client has a minimum requirement of Java 7. Hence, you need to include the following properties in your pom:

<maven.compiler.target>1.7</maven.compiler.target>
<maven.compiler.source>1.7</maven.compiler.source>

JavaScript - Hello world

This web application has been designed to introduce the principles of programming with Kurento for JavaScript developers. It consists on a WebRTC video communication in mirror (loopback). This tutorial assumes you have basic knowledge of JavaScript, HTML and WebRTC. We also recommend reading the Introducing Kurento section before starting this tutorial.

注解

This tutorial has been configurated for using https. Follow these instructions for securing your application.

For the impatient: running this example

You’ll need to install Kurento Media Server before running this example. Read installation guide for further information.

Be sure to have installed Node.js and Bower in your system. In an Ubuntu machine, you can install both as follows:

curl -sL https://deb.nodesource.com/setup_4.x | sudo bash -
sudo apt-get install -y nodejs
sudo npm install -g bower

Due to Same-origin policy, this demo has to be served by a HTTP server. A very simple way of doing this is by means of an HTTP Node.js server which can be installed using npm :

sudo npm install http-server -g

You also need the source code of this demo. You can clone it from GitHub. Then start the HTTP server:

git clone https://github.com/Kurento/kurento-tutorial-js.git
cd kurento-tutorial-js/kurento-hello-world
git checkout 6.6.1
bower install
http-server -p 8443 -S -C keys/server.crt -K keys/server.key

Finally, access the application connecting to the URL https://localhost:8443/ through a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the parameter ws_uri to the URL, as follows:

https://localhost:8443/index.html?ws_uri=wss://kms_host:kms_port/kurento

Notice that the Kurento Media Server must connected using a Secure WebSocket (i.e., the KMS URI starts with wss://). For this reason, the support for secure WebSocket must be enabled in the Kurento Media Server you are using to run this tutorial. For further information about securing applications, please visit the following page.

Understanding this example

Kurento provides developers a Kurento JavaScript Client to control Kurento Media Server. This client library can be used in any kind of JavaScript application including desktop and mobile browsers.

This hello world demo is one of the simplest web applications you can create with Kurento. The following picture shows an screenshot of this demo running:

Kurento Hello World Screenshot: WebRTC in loopback

Kurento Hello World Screenshot: WebRTC in loopback

The interface of the application (an HTML web page) is composed by two HTML5 video tags: one showing the local stream (as captured by the device webcam) and the other showing the remote stream sent by the media server back to the client.

The logic of the application is quite simple: the local stream is sent to the Kurento Media Server, which sends it back to the client without modifications. To implement this behavior, we need to create a Media Pipeline composed by a single Media Element, i.e. a WebRtcEndpoint, which holds the capability of exchanging full-duplex (bidirectional) WebRTC media flows. This media element is connected to itself,, so that the media it receives (from browser) is send back (to browser). This media pipeline is illustrated in the following picture:

Kurento Hello World Media Pipeline in context

Kurento Hello World Media Pipeline in context

This is a web application, and therefore it follows a client-server architecture. Nevertheless, due to the fact that we are using the Kurento JavaScript client, there is not need to use an application server since all the application logic is held by the browser. The Kurento JavaScript Client is used directly to control Kurento Media Server by means of a WebSocket bidirectional connection:

Complete sequence diagram of Kurento Hello World (WebRTC in loopbak) demo

Complete sequence diagram of Kurento Hello World (WebRTC in loopbak) demo

The following sections analyze in deep the client-side (JavaScript) code of this application, the dependencies, and how to run the demo. The complete source code can be found in GitHub.

JavaScript Logic

The Kurento hello-world demo follows a Single Page Application architecture (SPA). The interface is the following HTML page: index.html. This web page links two Kurento JavaScript libraries:

  • kurento-client.js : Implementation of the Kurento JavaScript Client.
  • kurento-utils.js : Kurento utility library aimed to simplify the WebRTC management in the browser.

In addition, these two JavaScript libraries are also required:

  • Bootstrap : Web framework for developing responsive web sites.
  • jquery.js : Cross-platform JavaScript library designed to simplify the client-side scripting of HTML.
  • adapter.js : WebRTC JavaScript utility library maintained by Google that abstracts away browser differences.
  • ekko-lightbox : Module for Bootstrap to open modal images, videos, and galleries.
  • demo-console : Custom JavaScript console.

The specific logic of the Hello World JavaScript demo is coded in the following JavaScript file: index.js. In this file, there is a function which is called when the green button labeled as Start in the GUI is clicked.

var startButton = document.getElementById("start");

startButton.addEventListener("click", function() {
   var options = {
     localVideo: videoInput,
     remoteVideo: videoOutput
   };

   webRtcPeer = kurentoUtils.WebRtcPeer.WebRtcPeerSendrecv(options, function(error) {
      if(error) return onError(error)
      this.generateOffer(onOffer)
   });

   [...]
}

The function WebRtcPeer.WebRtcPeerSendrecv abstracts the WebRTC internal details (i.e. PeerConnection and getUserStream) and makes possible to start a full-duplex WebRTC communication, using the HTML video tag with id videoInput to show the video camera (local stream) and the video tag videoOutput to show the remote stream provided by the Kurento Media Server.

Inside this function, a call to generateOffer is performed. This function accepts a callback in which the SDP offer is received. In this callback we create an instance of the KurentoClient class that will manage communications with the Kurento Media Server. So, we need to provide the URI of its WebSocket endpoint. In this example, we assume it’s listening in port 8888 at the same host than the HTTP serving the application.

[...]

var args = getopts(location.search,
{
  default:
  {
    ws_uri: 'ws://' + location.hostname + ':8888/kurento',
    ice_servers: undefined
  }
});

[...]

kurentoClient(args.ws_uri, function(error, client){
  [...]
};

Once we have an instance of kurentoClient, we need to create a Media Pipeline, as follows:

client.create("MediaPipeline", function(error, _pipeline){
   [...]
});

If everything works correctly, we will have an instance of a media pipeline (variable _pipeline in this example). With it, we are able to create Media Elements. In this example we just need a single WebRtcEndpoint.

In WebRTC, SDP is used for negotiating media exchanges between applications. Such negotiation happens based on the SDP offer and answer exchange mechanism by gathering the ICE candidates as follows:

pipeline = _pipeline;

pipeline.create("WebRtcEndpoint", function(error, webRtc){
   if(error) return onError(error);

   setIceCandidateCallbacks(webRtcPeer, webRtc, onError)

   webRtc.processOffer(sdpOffer, function(error, sdpAnswer){
     if(error) return onError(error);

     webRtcPeer.processAnswer(sdpAnswer, onError);
   });
   webRtc.gatherCandidates(onError);

   [...]
});

Finally, the WebRtcEndpoint is connected to itself (i.e., in loopback):

webRtc.connect(webRtc, function(error){
   if(error) return onError(error);

   console.log("Loopback established");
});

注解

The TURN and STUN servers to be used can be configured simple adding the parameter ice_servers to the application URL, as follows:

https://localhost:8443/index.html?ice_servers=[{"urls":"stun:stun1.example.net"},{"urls":"stun:stun2.example.net"}]
https://localhost:8443/index.html?ice_servers=[{"urls":"turn:turn.example.org","username":"user","credential":"myPassword"}]
Dependencies

All dependencies of this demo can to be obtained using Bower. The list of these dependencies are defined in the bower.json file, as follows:

"dependencies": {
   "kurento-client": "6.6.0",
   "kurento-utils": "6.6.2"
}

To get these dependencies, just run the following shell command:

bower install

注解

We are in active development. You can find the latest version of Kurento JavaScript Client at Bower.

Node.js - Hello world

This web application has been designed to introduce the principles of programming with Kurento for Node.js developers. It consists on a WebRTC video communication in mirror (loopback). This tutorial assumes you have basic knowledge of JavaScript, Node.js, HTML and WebRTC. We also recommend reading the Introducing Kurento section before starting this tutorial.

注解

This tutorial has been configurated for using https. Follow these instructions for securing your application.

For the impatient: running this example

You need to have installed the Kurento Media Server before running this example. Read the installation guide for further information.

Be sure to have installed Node.js and Bower in your system. In an Ubuntu machine, you can install both as follows:

curl -sL https://deb.nodesource.com/setup_4.x | sudo bash -
sudo apt-get install -y nodejs
sudo npm install -g bower

To launch the application, you need to clone the GitHub project where this demo is hosted, install it and run it:

git clone https://github.com/Kurento/kurento-tutorial-node.git
cd kurento-tutorial-node/kurento-hello-world
git checkout 6.6.1
npm install
npm start

If you have problems installing any of the dependencies, please remove them and clean the npm cache, and try to install them again:

rm -r node_modules
npm cache clean

Access the application connecting to the URL https://localhost:8443/ in a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the argument ws_uri to the npm execution command, as follows:

npm start -- --ws_uri=ws://kms_host:kms_port/kurento

In this case you need to use npm version 2. To update it you can use this command:

sudo npm install npm -g
Understanding this example

Kurento provides developers a Kurento JavaScript Client to control Kurento Media Server. This client library can be used from compatible JavaScript engines including browsers and Node.js.

This hello world demo is one of the simplest web application you can create with Kurento. The following picture shows an screenshot of this demo running:

Kurento Hello World Screenshot: WebRTC in loopback

Kurento Hello World Screenshot: WebRTC in loopback

The interface of the application (an HTML web page) is composed by two HTML5 video tags: one showing the local stream (as captured by the device webcam) and the other showing the remote stream sent by the media server back to the client.

The logic of the application is quite simple: the local stream is sent to the Kurento Media Server, which returns it back to the client without modifications. To implement this behavior we need to create a Media Pipeline composed by a single Media Element, i.e. a WebRtcEndpoint, which holds the capability of exchanging full-duplex (bidirectional) WebRTC media flows. This media element is connected to itself so that the media it receives (from browser) is send back (to browser). This media pipeline is illustrated in the following picture:

Kurento Hello World Media Pipeline in context

Kurento Hello World Media Pipeline in context

This is a web application, and therefore it follows a client-server architecture. At the client-side, the logic is implemented in JavaScript. At the server-side we use a Node.js application server consuming the Kurento JavaScript Client API to control Kurento Media Server capabilities. All in all, the high level architecture of this demo is three-tier. To communicate these entities, two WebSockets are used. First, a WebSocket is created between client and application server to implement a custom signaling protocol. Second, another WebSocket is used to perform the communication between the Kurento Java Client and the Kurento Media Server. This communication takes place using the Kurento Protocol. For further information on it, please see this page of the documentation.

The diagram below shows an complete sequence diagram from the interactions with the application interface to: i) JavaScript logic; ii) Application server logic (which uses the Kurento JavaScript Client); iii) Kurento Media Server.

Complete sequence diagram of Kurento Hello World (WebRTC in loopbak) demo

Complete sequence diagram of Kurento Hello World (WebRTC in loopbak) demo

The following sections analyze in deep the server and client-side code of this application. The complete source code can be found in GitHub.

Application Server Logic

This demo has been developed using the express framework for Node.js, but express is not a requirement for Kurento. The main script of this demo is server.js.

In order to communicate the JavaScript client and the Node application server a WebSocket is used. The incoming messages to this WebSocket (variable ws in the code) are conveniently handled to implemented the signaling protocol depicted in the figure before (i.e. messages start, stop, onIceCandidate).

var ws = require('ws');

[...]

var wss = new ws.Server({
    server : server,
    path : '/helloworld'
});

/*
 * Management of WebSocket messages
 */
wss.on('connection', function(ws) {
    var sessionId = null;
    var request = ws.upgradeReq;
    var response = {
        writeHead : {}
    };

    sessionHandler(request, response, function(err) {
        sessionId = request.session.id;
        console.log('Connection received with sessionId ' + sessionId);
    });

    ws.on('error', function(error) {
        console.log('Connection ' + sessionId + ' error');
        stop(sessionId);
    });

    ws.on('close', function() {
        console.log('Connection ' + sessionId + ' closed');
        stop(sessionId);
    });

    ws.on('message', function(_message) {
        var message = JSON.parse(_message);
        console.log('Connection ' + sessionId + ' received message ', message);

        switch (message.id) {
        case 'start':
            sessionId = request.session.id;
            start(sessionId, ws, message.sdpOffer, function(error, sdpAnswer) {
                if (error) {
                    return ws.send(JSON.stringify({
                        id : 'error',
                        message : error
                    }));
                }
                ws.send(JSON.stringify({
                    id : 'startResponse',
                    sdpAnswer : sdpAnswer
                }));
            });
            break;

        case 'stop':
            stop(sessionId);
            break;

        case 'onIceCandidate':
            onIceCandidate(sessionId, message.candidate);
            break;

        default:
            ws.send(JSON.stringify({
                id : 'error',
                message : 'Invalid message ' + message
            }));
            break;
        }

    });
});

In order to control the media capabilities provided by the Kurento Media Server, we need an instance of the KurentoClient in the Node application server. In order to create this instance, we need to specify to the client library the location of the Kurento Media Server. In this example, we assume it’s located at localhost listening in port 8888.

var kurento = require('kurento-client');

var kurentoClient = null;

var argv = minimist(process.argv.slice(2), {
    default: {
        as_uri: 'https://localhost:8443/',
        ws_uri: 'ws://localhost:8888/kurento'
    }
});

[...]

function getKurentoClient(callback) {
    if (kurentoClient !== null) {
        return callback(null, kurentoClient);
    }

    kurento(argv.ws_uri, function(error, _kurentoClient) {
        if (error) {
            console.log("Could not find media server at address " + argv.ws_uri);
            return callback("Could not find media server at address" + argv.ws_uri
                    + ". Exiting with error " + error);
        }

        kurentoClient = _kurentoClient;
        callback(null, kurentoClient);
    });
}

Once the Kurento Client has been instantiated, you are ready for communicating with Kurento Media Server. Our first operation is to create a Media Pipeline, then we need to create the Media Elements and connect them. In this example, we just need a single WebRtcEndpoint connected to itself (i.e. in loopback). These functions are called in the start function, which is fired when the start message is received:

function start(sessionId, ws, sdpOffer, callback) {
    if (!sessionId) {
        return callback('Cannot use undefined sessionId');
    }

    getKurentoClient(function(error, kurentoClient) {
        if (error) {
            return callback(error);
        }

        kurentoClient.create('MediaPipeline', function(error, pipeline) {
            if (error) {
                return callback(error);
            }

            createMediaElements(pipeline, ws, function(error, webRtcEndpoint) {
                if (error) {
                    pipeline.release();
                    return callback(error);
                }

                if (candidatesQueue[sessionId]) {
                    while(candidatesQueue[sessionId].length) {
                        var candidate = candidatesQueue[sessionId].shift();
                        webRtcEndpoint.addIceCandidate(candidate);
                    }
                }

                connectMediaElements(webRtcEndpoint, function(error) {
                    if (error) {
                        pipeline.release();
                        return callback(error);
                    }

                    webRtcEndpoint.on('OnIceCandidate', function(event) {
                        var candidate = kurento.getComplexType('IceCandidate')(event.candidate);
                        ws.send(JSON.stringify({
                            id : 'iceCandidate',
                            candidate : candidate
                        }));
                    });

                    webRtcEndpoint.processOffer(sdpOffer, function(error, sdpAnswer) {
                        if (error) {
                            pipeline.release();
                            return callback(error);
                        }

                        sessions[sessionId] = {
                            'pipeline' : pipeline,
                            'webRtcEndpoint' : webRtcEndpoint
                        }
                        return callback(null, sdpAnswer);
                    });

                    webRtcEndpoint.gatherCandidates(function(error) {
                        if (error) {
                            return callback(error);
                        }
                    });
                });
            });
        });
    });
}

function createMediaElements(pipeline, ws, callback) {
    pipeline.create('WebRtcEndpoint', function(error, webRtcEndpoint) {
        if (error) {
            return callback(error);
        }

        return callback(null, webRtcEndpoint);
    });
}

 function connectMediaElements(webRtcEndpoint, callback) {
    webRtcEndpoint.connect(webRtcEndpoint, function(error) {
        if (error) {
            return callback(error);
        }
        return callback(null);
    });
}

As of Kurento Media Server 6.0, the WebRTC negotiation is done by exchanging ICE candidates between the WebRTC peers. To implement this protocol, the webRtcEndpoint receives candidates from the client in OnIceCandidate function. These candidates are stored in a queue when the webRtcEndpoint is not available yet. Then these candidates are added to the media element by calling to the addIceCandidate method.

var candidatesQueue = {};

[...]

function onIceCandidate(sessionId, _candidate) {
    var candidate = kurento.getComplexType('IceCandidate')(_candidate);

    if (sessions[sessionId]) {
        console.info('Sending candidate');
        var webRtcEndpoint = sessions[sessionId].webRtcEndpoint;
        webRtcEndpoint.addIceCandidate(candidate);
    }
    else {
        console.info('Queueing candidate');
        if (!candidatesQueue[sessionId]) {
            candidatesQueue[sessionId] = [];
        }
        candidatesQueue[sessionId].push(candidate);
    }
}
Client-Side Logic

Let’s move now to the client-side of the application. To call the previously created WebSocket service in the server-side, we use the JavaScript class WebSocket. We use a specific Kurento JavaScript library called kurento-utils.js to simplify the WebRTC interaction with the server. This library depends on adapter.js, which is a JavaScript WebRTC utility maintained by Google that abstracts away browser differences. Finally jquery.js is also needed in this application. These libraries are linked in the index.html web page, and are used in the index.js. In the following snippet we can see the creation of the WebSocket (variable ws) in the path /helloworld. Then, the onmessage listener of the WebSocket is used to implement the JSON signaling protocol in the client-side. Notice that there are three incoming messages to client: startResponse, error, and iceCandidate. Convenient actions are taken to implement each step in the communication.

var ws = new WebSocket('ws://' + location.host + '/helloworld');
var webRtcPeer;

const I_CAN_START = 0;
const I_CAN_STOP = 1;
const I_AM_STARTING = 2;

[...]

ws.onmessage = function(message) {
   var parsedMessage = JSON.parse(message.data);
   console.info('Received message: ' + message.data);

   switch (parsedMessage.id) {
   case 'startResponse':
      startResponse(parsedMessage);
      break;
   case 'error':
      if (state == I_AM_STARTING) {
         setState(I_CAN_START);
      }
      onError('Error message from server: ' + parsedMessage.message);
      break;
   case 'iceCandidate':
      webRtcPeer.addIceCandidate(parsedMessage.candidate)
      break;
   default:
      if (state == I_AM_STARTING) {
         setState(I_CAN_START);
      }
      onError('Unrecognized message', parsedMessage);
   }
}

In the function start the method WebRtcPeer.WebRtcPeerSendrecv of kurento-utils.js is used to create the webRtcPeer object, which is used to handle the WebRTC communication.

videoInput = document.getElementById('videoInput');
videoOutput = document.getElementById('videoOutput');

[...]

function start() {
   console.log('Starting video call ...')

   // Disable start button
   setState(I_AM_STARTING);
   showSpinner(videoInput, videoOutput);

   console.log('Creating WebRtcPeer and generating local sdp offer ...');

    var options = {
      localVideo: videoInput,
      remoteVideo: videoOutput,
      onicecandidate : onIceCandidate
    }

    webRtcPeer = kurentoUtils.WebRtcPeer.WebRtcPeerSendrecv(options, function(error) {
        if(error) return onError(error);
        this.generateOffer(onOffer);
    });
}

function onIceCandidate(candidate) {
      console.log('Local candidate' + JSON.stringify(candidate));

      var message = {
         id : 'onIceCandidate',
         candidate : candidate
      };
      sendMessage(message);
}

function onOffer(error, offerSdp) {
   if(error) return onError(error);

   console.info('Invoking SDP offer callback function ' + location.host);
   var message = {
      id : 'start',
      sdpOffer : offerSdp
   }
   sendMessage(message);
}
Dependencies

Server-side dependencies of this demo are managed using npm. Our main dependency is the Kurento Client JavaScript (kurento-client). The relevant part of the package.json file for managing this dependency is:

"dependencies": {
   [...]
   "kurento-client" : "6.6.0"
}

At the client side, dependencies are managed using Bower. Take a look to the bower.json file and pay attention to the following section:

"dependencies": {
   [...]
   "kurento-utils" : "6.6.2"
}

注解

We are in active development. You can find the latest version of Kurento JavaScript Client at npm and Bower.

WebRTC magic mirror

This web application consists on a WebRTC video communication in loopback, adding a funny hat over detected faces. This is an example of a computer vision and augmented reality filter.

Java - WebRTC magic mirror

This web application extends the Hello World Tutorial, adding media processing to the basic WebRTC loopback.

注解

This tutorial has been configured to use https. Follow the instructions to secure your application.

For the impatient: running this example

First of all, you should install Kurento Media Server to run this demo. Please visit the installation guide for further information.

To launch the application, you need to clone the GitHub project where this demo is hosted, and then run the main class:

git clone https://github.com/Kurento/kurento-tutorial-java.git
cd kurento-tutorial-java/kurento-magic-mirror
git checkout 6.6.2
mvn compile exec:java

The web application starts on port 8443 in the localhost by default. Therefore, open the URL https://localhost:8443/ in a WebRTC compliant browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the flag kms.url to the JVM executing the demo. As we’ll be using maven, you should execute the following command

mvn compile exec:java -Dkms.url=ws://kms_host:kms_port/kurento
Understanding this example

This application uses computer vision and augmented reality techniques to add a funny hat on top of faces. The following picture shows a screenshot of the demo running in a web browser:

Kurento Magic Mirror Screenshot: WebRTC with filter in loopback

Kurento Magic Mirror Screenshot: WebRTC with filter in loopback

The interface of the application (an HTML web page) is composed by two HTML5 video tags: one for the video camera stream (the local client-side stream) and other for the mirror (the remote stream). The video camera stream is sent to Kurento Media Server, which processes and sends it back to the client as a remote stream. To implement this, we need to create a Media Pipeline composed by the following Media Element s:

  • WebRtcEndpoint: Provides full-duplex (bidirectional) WebRTC capabilities.
  • FaceOverlay filter: Computer vision filter that detects faces in the video stream and puts an image on top of them. In this demo the filter is configured to put a Super Mario hat).
WebRTC with filter in loopback Media Pipeline

WebRTC with filter in loopback Media Pipeline

This is a web application, and therefore it follows a client-server architecture. At the client-side, the logic is implemented in JavaScript. At the client-side, the logic is implemented in JavaScript. At the server-side, we use a Spring-Boot based server application consuming the Kurento Java Client API, to control Kurento Media Server capabilities. All in all, the high level architecture of this demo is three-tier. To communicate these entities, two WebSockets are used. First, a WebSocket is created between client and application server to implement a custom signaling protocol. Second, another WebSocket is used to perform the communication between the Kurento Java Client and the Kurento Media Server. This communication takes place using the Kurento Protocol. For further information on it, please see this page of the documentation.

To communicate the client with the Java EE application server we have designed a simple signaling protocol based on JSON messages over WebSocket ‘s. The normal sequence between client and server is as follows: i) Client starts the Magic Mirror. ii) Client stops the Magic Mirror.

If any exception happens, server sends an error message to the client. The detailed message sequence between client and application server is depicted in the following picture:

One to one video call signaling protocol

One to one video call signaling protocol

As you can see in the diagram, an SDP and ICE candidates needs to be exchanged between client and server to establish the WebRTC session between the Kurento client and server. Specifically, the SDP negotiation connects the WebRtcPeer at the browser with the WebRtcEndpoint at the server. The complete source code of this demo can be found in GitHub.

Application Server Side

This demo has been developed using Java in the server-side, based on the Spring Boot framework, which embeds a Tomcat web server within the generated maven artifact, and thus simplifies the development and deployment process.

注解

You can use whatever Java server side technology you prefer to build web applications with Kurento. For example, a pure Java EE application, SIP Servlets, Play, Vert.x, etc. Here we chose Spring Boot for convenience.

In the following figure you can see a class diagram of the server side code:

Server-side class diagram of the MagicMirror app

Server-side class diagram of the MagicMirror app

The main class of this demo is named MagicMirrorApp. As you can see, the KurentoClient is instantiated in this class as a Spring Bean. This bean is used to create Kurento Media Pipelines, which are used to add media capabilities to your applications. In this instantiation we see that we need to specify to the client library the location of the Kurento Media Server. In this example, we assume it is located at localhost, listening in port 8888. If you reproduce this tutorial, you’ll need to insert the specific location of your Kurento Media Server instance there.

@EnableWebSocket
@SpringBootApplication
public class MagicMirrorApp implements WebSocketConfigurer {

   final static String DEFAULT_KMS_WS_URI = "ws://localhost:8888/kurento";

   @Bean
   public MagicMirrorHandler handler() {
      return new MagicMirrorHandler();
   }

   @Bean
   public KurentoClient kurentoClient() {
      return KurentoClient.create();
   }

   @Override
   public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
      registry.addHandler(handler(), "/magicmirror");
   }

   public static void main(String[] args) throws Exception {
      new SpringApplication(MagicMirrorApp.class).run(args);
   }
}

This web application follows a Single Page Application architecture (SPA), and uses a WebSocket to communicate client with application server by means of requests and responses. Specifically, the main app class implements the interface WebSocketConfigurer to register a WebSocketHanlder to process WebSocket requests in the path /magicmirror.

MagicMirrorHandler class implements TextWebSocketHandler to handle text WebSocket requests. The central piece of this class is the method handleTextMessage. This method implements the actions for requests, returning responses through the WebSocket. In other words, it implements the server part of the signaling protocol depicted in the previous sequence diagram.

In the designed protocol there are three different kinds of incoming messages to the Server : start, stop and onIceCandidates. These messages are treated in the switch clause, taking the proper steps in each case.

public class MagicMirrorHandler extends TextWebSocketHandler {

   private final Logger log = LoggerFactory.getLogger(MagicMirrorHandler.class);
   private static final Gson gson = new GsonBuilder().create();

   private final ConcurrentHashMap<String, UserSession> users = new ConcurrentHashMap<String, UserSession>();

   @Autowired
   private KurentoClient kurento;

   @Override
   public void handleTextMessage(WebSocketSession session, TextMessage message) throws Exception {
      JsonObject jsonMessage = gson.fromJson(message.getPayload(), JsonObject.class);

      log.debug("Incoming message: {}", jsonMessage);

      switch (jsonMessage.get("id").getAsString()) {
      case "start":
         start(session, jsonMessage);
         break;
      case "stop": {
         UserSession user = users.remove(session.getId());
         if (user != null) {
            user.release();
         }
         break;
      }
      case "onIceCandidate": {
         JsonObject jsonCandidate = jsonMessage.get("candidate").getAsJsonObject();

         UserSession user = users.get(session.getId());
         if (user != null) {
            IceCandidate candidate = new IceCandidate(jsonCandidate.get("candidate").getAsString(),
                  jsonCandidate.get("sdpMid").getAsString(), jsonCandidate.get("sdpMLineIndex").getAsInt());
            user.addCandidate(candidate);
         }
         break;
      }
      default:
         sendError(session, "Invalid message with id " + jsonMessage.get("id").getAsString());
         break;
      }
   }

   private void start(WebSocketSession session, JsonObject jsonMessage) {
      ...
   }

   private void sendError(WebSocketSession session, String message) {
      ...
   }
}

In the following snippet, we can see the start method. It handles the ICE candidates gathering, creates a Media Pipeline, creates the Media Elements (WebRtcEndpoint and FaceOverlayFilter) and make the connections among them. A startResponse message is sent back to the client with the SDP answer.

private void start(final WebSocketSession session, JsonObject jsonMessage) {
   try {
      // User session
      UserSession user = new UserSession();
      MediaPipeline pipeline = kurento.createMediaPipeline();
      user.setMediaPipeline(pipeline);
      WebRtcEndpoint webRtcEndpoint = new WebRtcEndpoint.Builder(pipeline).build();
      user.setWebRtcEndpoint(webRtcEndpoint);
      users.put(session.getId(), user);

      // ICE candidates
      webRtcEndpoint.addIceCandidateFoundListener(new EventListener<IceCandidateFoundEvent>() {
         @Override
         public void onEvent(IceCandidateFoundEvent event) {
            JsonObject response = new JsonObject();
            response.addProperty("id", "iceCandidate");
            response.add("candidate", JsonUtils.toJsonObject(event.getCandidate()));
            try {
               synchronized (session) {
                  session.sendMessage(new TextMessage(response.toString()));
               }
            } catch (IOException e) {
               log.debug(e.getMessage());
            }
         }
      });

      // Media logic
      FaceOverlayFilter faceOverlayFilter = new FaceOverlayFilter.Builder(pipeline).build();

      String appServerUrl = System.getProperty("app.server.url", MagicMirrorApp.DEFAULT_APP_SERVER_URL);
      faceOverlayFilter.setOverlayedImage(appServerUrl + "/img/mario-wings.png", -0.35F, -1.2F, 1.6F, 1.6F);

      webRtcEndpoint.connect(faceOverlayFilter);
      faceOverlayFilter.connect(webRtcEndpoint);

      // SDP negotiation (offer and answer)
      String sdpOffer = jsonMessage.get("sdpOffer").getAsString();
      String sdpAnswer = webRtcEndpoint.processOffer(sdpOffer);

      JsonObject response = new JsonObject();
      response.addProperty("id", "startResponse");
      response.addProperty("sdpAnswer", sdpAnswer);

      synchronized (session) {
         session.sendMessage(new TextMessage(response.toString()));
      }

      webRtcEndpoint.gatherCandidates();

   } catch (Throwable t) {
      sendError(session, t.getMessage());
   }
}

注解

Notice the hat URL is provided by the application server and consumed by the KMS. This logic is assuming that the application server is hosted in local (localhost), and by the default the hat URL is https://localhost:8443/img/mario-wings.png. If your application server is hosted in a different host, it can be easily changed by means of the configuration parameter app.server.url, for example:

mvn compile exec:java -Dapp.server.url=https://app_server_host:app_server_port

The sendError method is quite simple: it sends an error message to the client when an exception is caught in the server-side.

private void sendError(WebSocketSession session, String message) {
   try {
      JsonObject response = new JsonObject();
      response.addProperty("id", "error");
      response.addProperty("message", message);
      session.sendMessage(new TextMessage(response.toString()));
   } catch (IOException e) {
      log.error("Exception sending message", e);
   }
}
Client-Side

Let’s move now to the client-side of the application. To call the previously created WebSocket service in the server-side, we use the JavaScript class WebSocket. We use a specific Kurento JavaScript library called kurento-utils.js to simplify the WebRTC interaction with the server. This library depends on adapter.js, which is a JavaScript WebRTC utility maintained by Google that abstracts away browser differences. Finally jquery.js is also needed in this application.

These libraries are linked in the index.html web page, and are used in the index.js. In the following snippet we can see the creation of the WebSocket (variable ws) in the path /magicmirror. Then, the onmessage listener of the WebSocket is used to implement the JSON signaling protocol in the client-side. Notice that there are three incoming messages to client: startResponse, error, and iceCandidate. Convenient actions are taken to implement each step in the communication. For example, in functions start the function WebRtcPeer.WebRtcPeerSendrecv of kurento-utils.js is used to start a WebRTC communication.

var ws = new WebSocket('ws://' + location.host + '/magicmirror');

ws.onmessage = function(message) {
   var parsedMessage = JSON.parse(message.data);
   console.info('Received message: ' + message.data);

   switch (parsedMessage.id) {
   case 'startResponse':
      startResponse(parsedMessage);
      break;
   case 'error':
      if (state == I_AM_STARTING) {
         setState(I_CAN_START);
      }
      onError("Error message from server: " + parsedMessage.message);
      break;
   case 'iceCandidate':
       webRtcPeer.addIceCandidate(parsedMessage.candidate, function (error) {
         if (error) {
            console.error("Error adding candidate: " + error);
            return;
         }
       });
       break;
   default:
      if (state == I_AM_STARTING) {
         setState(I_CAN_START);
      }
      onError('Unrecognized message', parsedMessage);
   }
}

function start() {
   console.log("Starting video call ...")
   // Disable start button
   setState(I_AM_STARTING);
   showSpinner(videoInput, videoOutput);

   console.log("Creating WebRtcPeer and generating local sdp offer ...");

    var options = {
         localVideo: videoInput,
         remoteVideo: videoOutput,
         onicecandidate: onIceCandidate
       }
   webRtcPeer = new kurentoUtils.WebRtcPeer.WebRtcPeerSendrecv(options,
      function (error) {
        if (error) {
           return console.error(error);
        }
        webRtcPeer.generateOffer(onOffer);
      });
}

function onOffer(offerSdp) {
   console.info('Invoking SDP offer callback function ' + location.host);
   var message = {
      id : 'start',
      sdpOffer : offerSdp
   }
   sendMessage(message);
}

function onIceCandidate(candidate) {
     console.log("Local candidate" + JSON.stringify(candidate));

     var message = {
       id: 'onIceCandidate',
       candidate: candidate
     };
     sendMessage(message);
}
Dependencies

This Java Spring application is implemented using Maven. The relevant part of the pom.xml is where Kurento dependencies are declared. As the following snippet shows, we need two dependencies: the Kurento Client Java dependency (kurento-client) and the JavaScript Kurento utility library (kurento-utils) for the client-side. Other client libraries are managed with webjars:

<dependencies>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-client</artifactId>
   </dependency>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-utils-js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars</groupId>
      <artifactId>webjars-locator</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>bootstrap</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>demo-console</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>adapter.js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>jquery</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>ekko-lightbox</artifactId>
   </dependency>
</dependencies>

注解

We are in active development. You can find the latest version of Kurento Java Client at Maven Central.

Kurento Java Client has a minimum requirement of Java 7. Hence, you need to include the following properties in your pom:

<maven.compiler.target>1.7</maven.compiler.target>
<maven.compiler.source>1.7</maven.compiler.source>

JavaScript - Magic Mirror

This web application extends the Hello World Tutorial, adding media processing to the basic WebRTC loopback.

注解

This tutorial has been configurated for using https. Follow these instructions for securing your application.

For the impatient: running this example

You’ll need to install Kurento Media Server before running this example. Read installation guide for further information.

Be sure to have installed Node.js and Bower in your system. In an Ubuntu machine, you can install both as follows:

curl -sL https://deb.nodesource.com/setup_4.x | sudo bash -
sudo apt-get install -y nodejs
sudo npm install -g bower

Due to Same-origin policy, this demo has to be served by an HTTP server. A very simple way of doing this is by means of an HTTP Node.js server which can be installed using npm :

sudo npm install http-server -g

You also need the source code of this demo. You can clone it from GitHub. Then start the HTTP server:

git clone https://github.com/Kurento/kurento-tutorial-js.git
cd kurento-tutorial-js/kurento-magic-mirror
git checkout 6.6.1
bower install
http-server -p 8443 -S -C keys/server.crt -K keys/server.key

Finally, access the application connecting to the URL https://localhost:8443/ through a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. Kurento Media Server must use WebSockets over SSL/TLS (WSS), so make sure you check this too. It is possible to locate the KMS in other machine simple adding the parameter ws_uri to the URL:

https://localhost:8443/index.html?ws_uri=wss://kms_host:kms_port/kurento

Notice that the Kurento Media Server must connected using a Secure WebSocket (i.e., the KMS URI starts with wss://). For this reason, the support for secure WebSocket must be enabled in the Kurento Media Server you are using to run this tutorial. For further information about securing applications, please visit the following page.

Understanding this example

This application uses computer vision and augmented reality techniques to add a funny hat on top of detected faces. The following picture shows a screenshot of the demo running in a web browser:

Kurento Magic Mirror Screenshot: WebRTC with filter in loopback

Kurento Magic Mirror Screenshot: WebRTC with filter in loopback

The interface of the application (an HTML web page) is composed by two HTML5 video tags: one for the video camera stream (the local client-side stream) and other for the mirror (the remote stream). The video camera stream is sent to the Kurento Media Server, processed and then is returned to the client as a remote stream.

To implement this, we need to create a Media Pipeline composed by the following Media Element s:

  • WebRtcEndpoint: Provides full-duplex (bidirectional) WebRTC capabilities.
  • FaceOverlay filter: Computer vision filter that detects faces in the video stream and puts an image on top of them. In this demo the filter is configured to put a Super Mario hat).

The media pipeline implemented is illustrated in the following picture:

WebRTC with filter in loopback Media Pipeline

WebRTC with filter in loopback Media Pipeline

The complete source code of this demo can be found in GitHub.

JavaScript Logic

This demo follows a Single Page Application architecture (SPA). The interface is the following HTML page: index.html. This web page links two Kurento JavaScript libraries:

  • kurento-client.js : Implementation of the Kurento JavaScript Client.
  • kurento-utils.js : Kurento utility library aimed to simplify the WebRTC management in the browser.

In addition, these two JavaScript libraries are also required:

  • Bootstrap : Web framework for developing responsive web sites.
  • jquery.js : Cross-platform JavaScript library designed to simplify the client-side scripting of HTML.
  • adapter.js : WebRTC JavaScript utility library maintained by Google that abstracts away browser differences.
  • ekko-lightbox : Module for Bootstrap to open modal images, videos, and galleries.
  • demo-console : Custom JavaScript console.

The specific logic of this demo is coded in the following JavaScript page: index.js. In this file, there is a function which is called when the green button labeled as Start in the GUI is clicked.

var startButton = document.getElementById("start");

startButton.addEventListener("click", function() {
   var options = {
     localVideo: videoInput,
     remoteVideo: videoOutput
   };

   webRtcPeer = kurentoUtils.WebRtcPeer.WebRtcPeerSendrecv(options, function(error) {
      if(error) return onError(error)
      this.generateOffer(onOffer)
   });

   [...]
}

The function WebRtcPeer.WebRtcPeerSendrecv abstracts the WebRTC internal details (i.e. PeerConnection and getUserStream) and makes possible to start a full-duplex WebRTC communication, using the HTML video tag with id videoInput to show the video camera (local stream) and the video tag videoOutput to show the remote stream provided by the Kurento Media Server.

Inside this function, a call to generateOffer is performed. This function accepts a callback in which the SDP offer is received. In this callback we create an instance of the KurentoClient class that will manage communications with the Kurento Media Server. So, we need to provide the URI of its WebSocket endpoint. In this example, we assume it’s listening in port 8888 at the same host than the HTTP serving the application.

[...]

var args = getopts(location.search,
{
  default:
  {
    ws_uri: 'ws://' + location.hostname + ':8888/kurento',
    ice_servers: undefined
  }
});

[...]

kurentoClient(args.ws_uri, function(error, client){
  [...]
};

Once we have an instance of kurentoClient, the following step is to create a Media Pipeline, as follows:

client.create("MediaPipeline", function(error, _pipeline){
   [...]
});

If everything works correctly, we have an instance of a media pipeline (variable pipeline in this example). With this instance, we are able to create Media Elements. In this example we just need a WebRtcEndpoint and a FaceOverlayFilter. Then, these media elements are interconnected:

pipeline.create('WebRtcEndpoint', function(error, webRtcEp) {
  if (error) return onError(error);

  setIceCandidateCallbacks(webRtcPeer, webRtcEp, onError)

  webRtcEp.processOffer(sdpOffer, function(error, sdpAnswer) {
    if (error) return onError(error);

    webRtcPeer.processAnswer(sdpAnswer, onError);
  });
  webRtcEp.gatherCandidates(onError);

  pipeline.create('FaceOverlayFilter', function(error, filter) {
    if (error) return onError(error);

    filter.setOverlayedImage(args.hat_uri, -0.35, -1.2, 1.6, 1.6,
    function(error) {
      if (error) return onError(error);

    });

    client.connect(webRtcEp, filter, webRtcEp, function(error) {
      if (error) return onError(error);

      console.log("WebRtcEndpoint --> filter --> WebRtcEndpoint");
    });
  });
});

注解

The TURN and STUN servers to be used can be configured simple adding the parameter ice_servers to the application URL, as follows:

https://localhost:8443/index.html?ice_servers=[{"urls":"stun:stun1.example.net"},{"urls":"stun:stun2.example.net"}]
https://localhost:8443/index.html?ice_servers=[{"urls":"turn:turn.example.org","username":"user","credential":"myPassword"}]
Dependencies

The dependencies of this demo has to be obtained using Bower. The definition of these dependencies are defined in the bower.json file, as follows:

"dependencies": {
   "kurento-client": "6.6.0",
   "kurento-utils": "6.6.2"
}

注解

We are in active development. You can find the latest version of Kurento JavaScript Client at Bower.

Node.js - WebRTC magic mirror

This web application extends the Hello World Tutorial, adding media processing to the basic WebRTC loopback.

注解

This tutorial has been configurated for using https. Follow these instructions for securing your application.

For the impatient: running this example

First of all, you should install Kurento Media Server to run this demo. Please visit the installation guide for further information.

Be sure to have installed Node.js and Bower in your system. In an Ubuntu machine, you can install both as follows:

curl -sL https://deb.nodesource.com/setup_4.x | sudo bash -
sudo apt-get install -y nodejs
sudo npm install -g bower

To launch the application, you need to clone the GitHub project where this demo is hosted, install it and run it:

git clone https://github.com/Kurento/kurento-tutorial-node.git
cd kurento-tutorial-node/kurento-magic-mirror
git checkout 6.6.1
npm install
npm start

If you have problems installing any of the dependencies, please remove them and clean the npm cache, and try to install them again:

rm -r node_modules
npm cache clean

Access the application connecting to the URL https://localhost:8443/ in a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the argument ws_uri to the npm execution command, as follows:

npm start -- --ws_uri=ws://kms_host:kms_port/kurento

In this case you need to use npm version 2. To update it you can use this command:

sudo npm install npm -g
Understanding this example

This application uses computer vision and augmented reality techniques to add a funny hat on top of faces. The following picture shows a screenshot of the demo running in a web browser:

Kurento Magic Mirror Screenshot: WebRTC with filter in loopback

Kurento Magic Mirror Screenshot: WebRTC with filter in loopback

The interface of the application (an HTML web page) is composed by two HTML5 video tags: one for the video camera stream (the local client-side stream) and other for the mirror (the remote stream). The video camera stream is sent to Kurento Media Server, which processes and sends it back to the client as a remote stream. To implement this, we need to create a Media Pipeline composed by the following Media Element s:

  • WebRtcEndpoint: Provides full-duplex (bidirectional) WebRTC capabilities.
  • FaceOverlay filter: Computer vision filter that detects faces in the video stream and puts an image on top of them. In this demo the filter is configured to put a Super Mario hat).
WebRTC with filter in loopback Media Pipeline

WebRTC with filter in loopback Media Pipeline

This is a web application, and therefore it follows a client-server architecture. At the client-side, the logic is implemented in JavaScript. At the server-side we use a Node.js application server consuming the Kurento JavaScript Client API to control Kurento Media Server capabilities. All in all, the high level architecture of this demo is three-tier. To communicate these entities, two WebSockets are used. First, a WebSocket is created between client and application server to implement a custom signaling protocol. Second, another WebSocket is used to perform the communication between the Kurento JavaScript Client and the Kurento Media Server. This communication takes place using the Kurento Protocol. For further information on it, please see this page of the documentation.

To communicate the client with the Node.js application server we have designed a simple signaling protocol based on JSON messages over WebSocket ‘s. The normal sequence between client and server is as follows: i) Client starts the Magic Mirror. ii) Client stops the Magic Mirror.

If any exception happens, server sends an error message to the client. The detailed message sequence between client and application server is depicted in the following picture:

One to one video call signaling protocol

One to one video call signaling protocol

As you can see in the diagram, an SDP and ICE candidates needs to be exchanged between client and server to establish the WebRTC session between the Kurento client and server. Specifically, the SDP negotiation connects the WebRtcPeer at the browser with the WebRtcEndpoint at the server. The complete source code of this demo can be found in GitHub.

Application Server Logic

This demo has been developed using the express framework for Node.js, but express is not a requirement for Kurento. The main script of this demo is server.js.

In order to communicate the JavaScript client and the Node application server a WebSocket is used. The incoming messages to this WebSocket (variable ws in the code) are conveniently handled to implemented the signaling protocol depicted in the figure before (i.e. messages start, stop, onIceCandidate).

var ws = require('ws');

[...]

var wss = new ws.Server({
    server : server,
    path : '/magicmirror'
});

/*
 * Management of WebSocket messages
 */
wss.on('connection', function(ws) {
    var sessionId = null;
    var request = ws.upgradeReq;
    var response = {
        writeHead : {}
    };

    sessionHandler(request, response, function(err) {
        sessionId = request.session.id;
        console.log('Connection received with sessionId ' + sessionId);
    });

    ws.on('error', function(error) {
        console.log('Connection ' + sessionId + ' error');
        stop(sessionId);
    });

    ws.on('close', function() {
        console.log('Connection ' + sessionId + ' closed');
        stop(sessionId);
    });

    ws.on('message', function(_message) {
        var message = JSON.parse(_message);
        console.log('Connection ' + sessionId + ' received message ', message);

        switch (message.id) {
        case 'start':
            sessionId = request.session.id;
            start(sessionId, ws, message.sdpOffer, function(error, sdpAnswer) {
                if (error) {
                    return ws.send(JSON.stringify({
                        id : 'error',
                        message : error
                    }));
                }
                ws.send(JSON.stringify({
                    id : 'startResponse',
                    sdpAnswer : sdpAnswer
                }));
            });
            break;

        case 'stop':
            stop(sessionId);
            break;

        case 'onIceCandidate':
            onIceCandidate(sessionId, message.candidate);
            break;

        default:
            ws.send(JSON.stringify({
                id : 'error',
                message : 'Invalid message ' + message
            }));
            break;
        }

    });
});

In order to control the media capabilities provided by the Kurento Media Server, we need an instance of the KurentoClient in the Node application server. In order to create this instance, we need to specify to the client library the location of the Kurento Media Server. In this example, we assume it’s located at localhost listening in port 8888.

var kurento = require('kurento-client');

var kurentoClient = null;

var argv = minimist(process.argv.slice(2), {
    default: {
        as_uri: 'https://localhost:8443/',
        ws_uri: 'ws://localhost:8888/kurento'
    }
});

[...]

function getKurentoClient(callback) {
    if (kurentoClient !== null) {
        return callback(null, kurentoClient);
    }

    kurento(argv.ws_uri, function(error, _kurentoClient) {
        if (error) {
            console.log("Could not find media server at address " + argv.ws_uri);
            return callback("Could not find media server at address" + argv.ws_uri
                    + ". Exiting with error " + error);
        }

        kurentoClient = _kurentoClient;
        callback(null, kurentoClient);
    });
}

Once the Kurento Client has been instantiated, you are ready for communicating with Kurento Media Server. Our first operation is to create a Media Pipeline, then we need to create the Media Elements and connect them. In this example, we need a WebRtcEndpoint connected to a FaceOverlayFilter, which is connected to the sink of the same WebRtcEndpoint. These functions are called in the start function, which is fired when the start message is received:

function start(sessionId, ws, sdpOffer, callback) {
    if (!sessionId) {
        return callback('Cannot use undefined sessionId');
    }

    getKurentoClient(function(error, kurentoClient) {
        if (error) {
            return callback(error);
        }

        kurentoClient.create('MediaPipeline', function(error, pipeline) {
            if (error) {
                return callback(error);
            }

            createMediaElements(pipeline, ws, function(error, webRtcEndpoint) {
                if (error) {
                    pipeline.release();
                    return callback(error);
                }

                if (candidatesQueue[sessionId]) {
                    while(candidatesQueue[sessionId].length) {
                        var candidate = candidatesQueue[sessionId].shift();
                        webRtcEndpoint.addIceCandidate(candidate);
                    }
                }

                connectMediaElements(webRtcEndpoint, faceOverlayFilter, function(error) {
                    if (error) {
                        pipeline.release();
                        return callback(error);
                    }

                    webRtcEndpoint.on('OnIceCandidate', function(event) {
                        var candidate = kurento.getComplexType('IceCandidate')(event.candidate);
                        ws.send(JSON.stringify({
                            id : 'iceCandidate',
                            candidate : candidate
                        }));
                    });

                    webRtcEndpoint.processOffer(sdpOffer, function(error, sdpAnswer) {
                        if (error) {
                            pipeline.release();
                            return callback(error);
                        }

                        sessions[sessionId] = {
                            'pipeline' : pipeline,
                            'webRtcEndpoint' : webRtcEndpoint
                        }
                        return callback(null, sdpAnswer);
                    });

                    webRtcEndpoint.gatherCandidates(function(error) {
                        if (error) {
                            return callback(error);
                        }
                    });
                });
            });
        });
    });
}

function createMediaElements(pipeline, ws, callback) {
    pipeline.create('WebRtcEndpoint', function(error, webRtcEndpoint) {
        if (error) {
            return callback(error);
        }

        return callback(null, webRtcEndpoint);
    });
}

function connectMediaElements(webRtcEndpoint, faceOverlayFilter, callback) {
    webRtcEndpoint.connect(faceOverlayFilter, function(error) {
        if (error) {
            return callback(error);
        }

        faceOverlayFilter.connect(webRtcEndpoint, function(error) {
            if (error) {
                return callback(error);
            }

            return callback(null);
        });
    });
}

As of Kurento Media Server 6.0, the WebRTC negotiation is done by exchanging ICE candidates between the WebRTC peers. To implement this protocol, the webRtcEndpoint receives candidates from the client in OnIceCandidate function. These candidates are stored in a queue when the webRtcEndpoint is not available yet. Then these candidates are added to the media element by calling to the addIceCandidate method.

var candidatesQueue = {};

[...]

function onIceCandidate(sessionId, _candidate) {
    var candidate = kurento.getComplexType('IceCandidate')(_candidate);

    if (sessions[sessionId]) {
        console.info('Sending candidate');
        var webRtcEndpoint = sessions[sessionId].webRtcEndpoint;
        webRtcEndpoint.addIceCandidate(candidate);
    }
    else {
        console.info('Queueing candidate');
        if (!candidatesQueue[sessionId]) {
            candidatesQueue[sessionId] = [];
        }
        candidatesQueue[sessionId].push(candidate);
    }
}
Client-Side Logic

Let’s move now to the client-side of the application. To call the previously created WebSocket service in the server-side, we use the JavaScript class WebSocket. We use a specific Kurento JavaScript library called kurento-utils.js to simplify the WebRTC interaction with the server. This library depends on adapter.js, which is a JavaScript WebRTC utility maintained by Google that abstracts away browser differences. Finally jquery.js is also needed in this application. These libraries are linked in the index.html web page, and are used in the index.js. In the following snippet we can see the creation of the WebSocket (variable ws) in the path /magicmirror. Then, the onmessage listener of the WebSocket is used to implement the JSON signaling protocol in the client-side. Notice that there are three incoming messages to client: startResponse, error, and iceCandidate. Convenient actions are taken to implement each step in the communication.

var ws = new WebSocket('ws://' + location.host + '/magicmirror');
var webRtcPeer;

const I_CAN_START = 0;
const I_CAN_STOP = 1;
const I_AM_STARTING = 2;

[...]

ws.onmessage = function(message) {
   var parsedMessage = JSON.parse(message.data);
   console.info('Received message: ' + message.data);

   switch (parsedMessage.id) {
   case 'startResponse':
      startResponse(parsedMessage);
      break;
   case 'error':
      if (state == I_AM_STARTING) {
         setState(I_CAN_START);
      }
      onError('Error message from server: ' + parsedMessage.message);
      break;
   case 'iceCandidate':
      webRtcPeer.addIceCandidate(parsedMessage.candidate)
      break;
   default:
      if (state == I_AM_STARTING) {
         setState(I_CAN_START);
      }
      onError('Unrecognized message', parsedMessage);
   }
}

In the function start the method WebRtcPeer.WebRtcPeerSendrecv of kurento-utils.js is used to create the webRtcPeer object, which is used to handle the WebRTC communication.

videoInput = document.getElementById('videoInput');
videoOutput = document.getElementById('videoOutput');

[...]

function start() {
   console.log('Starting video call ...')

   // Disable start button
   setState(I_AM_STARTING);
   showSpinner(videoInput, videoOutput);

   console.log('Creating WebRtcPeer and generating local sdp offer ...');

    var options = {
      localVideo: videoInput,
      remoteVideo: videoOutput,
      onicecandidate : onIceCandidate
    }

    webRtcPeer = kurentoUtils.WebRtcPeer.WebRtcPeerSendrecv(options, function(error) {
        if(error) return onError(error);
        this.generateOffer(onOffer);
    });
}

function onIceCandidate(candidate) {
      console.log('Local candidate' + JSON.stringify(candidate));

      var message = {
         id : 'onIceCandidate',
         candidate : candidate
      };
      sendMessage(message);
}

function onOffer(error, offerSdp) {
   if(error) return onError(error);

   console.info('Invoking SDP offer callback function ' + location.host);
   var message = {
      id : 'start',
      sdpOffer : offerSdp
   }
   sendMessage(message);
}
Dependencies

Server-side dependencies of this demo are managed using npm. Our main dependency is the Kurento Client JavaScript (kurento-client). The relevant part of the package.json file for managing this dependency is:

"dependencies": {
   [...]
   "kurento-client" : "6.6.0"
}

At the client side, dependencies are managed using Bower. Take a look to the bower.json file and pay attention to the following section:

"dependencies": {
   [...]
   "kurento-utils" : "6.6.2"
}

注解

We are in active development. You can find the latest version of Kurento JavaScript Client at npm and Bower.

WebRTC one-to-many broadcast

Video broadcasting for WebRTC. One peer transmits a video stream and N peers receive it.

Java - One to many video call

This web application consists on a one-to-many video call using WebRTC technology. In other words, it is an implementation of a video broadcasting web application.

注解

This tutorial has been configured to use https. Follow the instructions to secure your application.

For the impatient: running this example

First of all, you should install Kurento Media Server to run this demo. Please visit the installation guide for further information.

To launch the application, you need to clone the GitHub project where this demo is hosted, and then run the main class:

git clone https://github.com/Kurento/kurento-tutorial-java.git
cd kurento-tutorial-java/kurento-one2many-call
git checkout 6.6.2
mvn compile exec:java

The web application starts on port 8443 in the localhost by default. Therefore, open the URL https://localhost:8443/ in a WebRTC compliant browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the flag kms.url to the JVM executing the demo. As we’ll be using maven, you should execute the following command

mvn compile exec:java -Dkms.url=ws://kms_host:kms_port/kurento
Understanding this example

There will be two types of users in this application: 1 peer sending media (let’s call it Presenter) and N peers receiving the media from the Presenter (let’s call them Viewers). Thus, the Media Pipeline is composed by 1+N interconnected WebRtcEndpoints. The following picture shows an screenshot of the Presenter’s web GUI:

One to many video call screenshot

One to many video call screenshot

To implement this behavior we have to create a Media Pipeline composed by 1+N WebRtcEndpoints. The Presenter peer sends its stream to the rest of the Viewers. Viewers are configured in receive-only mode. The implemented media pipeline is illustrated in the following picture:

One to many video call Media Pipeline

One to many video call Media Pipeline

This is a web application, and therefore it follows a client-server architecture. At the client-side, the logic is implemented in JavaScript. At the server-side, we use a Spring-Boot based server application consuming the Kurento Java Client API, to control Kurento Media Server capabilities. All in all, the high level architecture of this demo is three-tier. To communicate these entities two WebSockets are used. First, a WebSocket is created between client and server-side to implement a custom signaling protocol. Second, another WebSocket is used to perform the communication between the Kurento Java Client and the Kurento Media Server. This communication is implemented by the Kurento Protocol. For further information, please see this page.

Client and application server communicate using a signaling protocol based on JSON messages over WebSocket ‘s. The normal sequence between client and server is as follows:

1. A Presenter enters in the system. There must be one and only one Presenter at any time. For that, if a Presenter has already present, an error message is sent if another user tries to become Presenter.

2. N Viewers connect to the presenter. If no Presenter is present, then an error is sent to the corresponding Viewer.

  1. Viewers can leave the communication at any time.

4. When the Presenter finishes the session each connected Viewer receives an stopCommunication message and also terminates its session.

We can draw the following sequence diagram with detailed messages between clients and server:

One to many video call signaling protocol

One to many video call signaling protocol

As you can see in the diagram, SDP and ICE candidates need to be exchanged between client and server to establish the WebRTC connection between the Kurento client and server. Specifically, the SDP negotiation connects the WebRtcPeer in the browser with the WebRtcEndpoint in the server. The complete source code of this demo can be found in GitHub.

Application Server Logic

This demo has been developed using Java in the server-side, based on the Spring Boot framework, which embeds a Tomcat web server within the generated maven artifact, and thus simplifies the development and deployment process.

注解

You can use whatever Java server side technology you prefer to build web applications with Kurento. For example, a pure Java EE application, SIP Servlets, Play, Vertex, etc. We chose Spring Boot for convenience.

In the following, figure you can see a class diagram of the server side code:

Server-side class diagram of the One2Many app

Server-side class diagram of the One2Many app

The main class of this demo is named One2ManyCallApp. As you can see, the KurentoClient is instantiated in this class as a Spring Bean. This bean is used to create Kurento Media Pipelines, which are used to add media capabilities to your applications. In this instantiation we see that a WebSocket is used to connect with Kurento Media Server, by default in the localhost and listening in the port 8888.

@EnableWebSocket
@SpringBootApplication
public class One2ManyCallApp implements WebSocketConfigurer {

   @Bean
   public CallHandler callHandler() {
      return new CallHandler();
   }

   @Bean
   public KurentoClient kurentoClient() {
      return KurentoClient.create();
   }

   public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
      registry.addHandler(callHandler(), "/call");
   }

   public static void main(String[] args) throws Exception {
      new SpringApplication(One2ManyCallApp.class).run(args);
   }

}

This web application follows a Single Page Application architecture (SPA), and uses a WebSocket to communicate client with server by means of requests and responses. Specifically, the main app class implements the interface WebSocketConfigurer to register a WebSocketHanlder to process WebSocket requests in the path /call.

CallHandler class implements TextWebSocketHandler to handle text WebSocket requests. The central piece of this class is the method handleTextMessage. This method implements the actions for requests, returning responses through the WebSocket. In other words, it implements the server part of the signaling protocol depicted in the previous sequence diagram.

In the designed protocol there are three different kind of incoming messages to the Server : presenter, viewer, stop, and onIceCandidate. These messages are treated in the switch clause, taking the proper steps in each case.

public class CallHandler extends TextWebSocketHandler {

   private static final Logger log = LoggerFactory.getLogger(CallHandler.class);
   private static final Gson gson = new GsonBuilder().create();

   private final ConcurrentHashMap<String, UserSession> viewers = new ConcurrentHashMap<String, UserSession>();

   @Autowired
   private KurentoClient kurento;

   private MediaPipeline pipeline;
   private UserSession presenterUserSession;

   @Override
   public void handleTextMessage(WebSocketSession session, TextMessage message) throws Exception {
      JsonObject jsonMessage = gson.fromJson(message.getPayload(), JsonObject.class);
      log.debug("Incoming message from session '{}': {}", session.getId(), jsonMessage);

      switch (jsonMessage.get("id").getAsString()) {
      case "presenter":
         try {
            presenter(session, jsonMessage);
         } catch (Throwable t) {
            handleErrorResponse(t, session, "presenterResponse");
         }
         break;
      case "viewer":
         try {
            viewer(session, jsonMessage);
         } catch (Throwable t) {
            handleErrorResponse(t, session, "viewerResponse");
         }
         break;
      case "onIceCandidate": {
         JsonObject candidate = jsonMessage.get("candidate").getAsJsonObject();

         UserSession user = null;
         if (presenterUserSession != null) {
            if (presenterUserSession.getSession() == session) {
               user = presenterUserSession;
            } else {
               user = viewers.get(session.getId());
            }
         }
         if (user != null) {
            IceCandidate cand = new IceCandidate(candidate.get("candidate").getAsString(),
                  candidate.get("sdpMid").getAsString(), candidate.get("sdpMLineIndex").getAsInt());
            user.addCandidate(cand);
         }
         break;
      }
      case "stop":
         stop(session);
         break;
      default:
         break;
      }
   }

   private void handleErrorResponse(Throwable t, WebSocketSession session,
         String responseId) throws IOException {
      stop(session);
      log.error(t.getMessage(), t);
      JsonObject response = new JsonObject();
      response.addProperty("id", responseId);
      response.addProperty("response", "rejected");
      response.addProperty("message", t.getMessage());
      session.sendMessage(new TextMessage(response.toString()));
   }

   private synchronized void presenter(final WebSocketSession session, JsonObject jsonMessage) throws IOException {
      ...
   }

   private synchronized void viewer(final WebSocketSession session, JsonObject jsonMessage) throws IOException {
      ...
   }

   private synchronized void stop(WebSocketSession session) throws IOException {
      ...
   }

   @Override
   public void afterConnectionClosed(WebSocketSession session, CloseStatus status) throws Exception {
      stop(session);
   }

}

In the following snippet, we can see the presenter method. It creates a Media Pipeline and the WebRtcEndpoint for presenter:

private synchronized void presenter(final WebSocketSession session, JsonObject jsonMessage) throws IOException {
   if (presenterUserSession == null) {
      presenterUserSession = new UserSession(session);

      pipeline = kurento.createMediaPipeline();
      presenterUserSession.setWebRtcEndpoint(new WebRtcEndpoint.Builder(pipeline).build());

      WebRtcEndpoint presenterWebRtc = presenterUserSession.getWebRtcEndpoint();

      presenterWebRtc.addIceCandidateFoundListener(new EventListener<IceCandidateFoundEvent>() {

         @Override
         public void onEvent(IceCandidateFoundEvent event) {
            JsonObject response = new JsonObject();
            response.addProperty("id", "iceCandidate");
            response.add("candidate", JsonUtils.toJsonObject(event.getCandidate()));
            try {
               synchronized (session) {
                  session.sendMessage(new TextMessage(response.toString()));
               }
            } catch (IOException e) {
               log.debug(e.getMessage());
            }
         }
      });

      String sdpOffer = jsonMessage.getAsJsonPrimitive("sdpOffer").getAsString();
      String sdpAnswer = presenterWebRtc.processOffer(sdpOffer);

      JsonObject response = new JsonObject();
      response.addProperty("id", "presenterResponse");
      response.addProperty("response", "accepted");
      response.addProperty("sdpAnswer", sdpAnswer);

      synchronized (session) {
         presenterUserSession.sendMessage(response);
      }
      presenterWebRtc.gatherCandidates();

   } else {
      JsonObject response = new JsonObject();
      response.addProperty("id", "presenterResponse");
      response.addProperty("response", "rejected");
      response.addProperty("message", "Another user is currently acting as sender. Try again later ...");
      session.sendMessage(new TextMessage(response.toString()));
   }
}

The viewer method is similar, but not he Presenter WebRtcEndpoint is connected to each of the viewers WebRtcEndpoints, otherwise an error is sent back to the client.

private synchronized void viewer(final WebSocketSession session, JsonObject jsonMessage) throws IOException {
   if (presenterUserSession == null || presenterUserSession.getWebRtcEndpoint() == null) {
      JsonObject response = new JsonObject();
      response.addProperty("id", "viewerResponse");
      response.addProperty("response", "rejected");
      response.addProperty("message", "No active sender now. Become sender or . Try again later ...");
      session.sendMessage(new TextMessage(response.toString()));
   } else {
      if (viewers.containsKey(session.getId())) {
         JsonObject response = new JsonObject();
         response.addProperty("id", "viewerResponse");
         response.addProperty("response", "rejected");
         response.addProperty("message",
               "You are already viewing in this session. Use a different browser to add additional viewers.");
         session.sendMessage(new TextMessage(response.toString()));
         return;
      }
      UserSession viewer = new UserSession(session);
      viewers.put(session.getId(), viewer);

      String sdpOffer = jsonMessage.getAsJsonPrimitive("sdpOffer").getAsString();

      WebRtcEndpoint nextWebRtc = new WebRtcEndpoint.Builder(pipeline).build();

      nextWebRtc.addIceCandidateFoundListener(new EventListener<IceCandidateFoundEvent>() {

         @Override
         public void onEvent(IceCandidateFoundEvent event) {
            JsonObject response = new JsonObject();
            response.addProperty("id", "iceCandidate");
            response.add("candidate", JsonUtils.toJsonObject(event.getCandidate()));
            try {
               synchronized (session) {
                  session.sendMessage(new TextMessage(response.toString()));
               }
            } catch (IOException e) {
               log.debug(e.getMessage());
            }
         }
      });

      viewer.setWebRtcEndpoint(nextWebRtc);
      presenterUserSession.getWebRtcEndpoint().connect(nextWebRtc);
      String sdpAnswer = nextWebRtc.processOffer(sdpOffer);

      JsonObject response = new JsonObject();
      response.addProperty("id", "viewerResponse");
      response.addProperty("response", "accepted");
      response.addProperty("sdpAnswer", sdpAnswer);

      synchronized (session) {
         viewer.sendMessage(response);
      }
      nextWebRtc.gatherCandidates();
   }
}

Finally, the stop message finishes the communication. If this message is sent by the Presenter, a stopCommunication message is sent to each connected Viewer:

private synchronized void stop(WebSocketSession session) throws IOException {
   String sessionId = session.getId();
   if (presenterUserSession != null && presenterUserSession.getSession().getId().equals(sessionId)) {
      for (UserSession viewer : viewers.values()) {
         JsonObject response = new JsonObject();
         response.addProperty("id", "stopCommunication");
         viewer.sendMessage(response);
      }

      log.info("Releasing media pipeline");
      if (pipeline != null) {
         pipeline.release();
      }
      pipeline = null;
      presenterUserSession = null;
   } else if (viewers.containsKey(sessionId)) {
      if (viewers.get(sessionId).getWebRtcEndpoint() != null) {
         viewers.get(sessionId).getWebRtcEndpoint().release();
      }
      viewers.remove(sessionId);
   }
}
Client-Side

Let’s move now to the client-side of the application. To call the previously created WebSocket service in the server-side, we use the JavaScript class WebSocket. We use a specific Kurento JavaScript library called kurento-utils.js to simplify the WebRTC interaction with the server. This library depends on adapter.js, which is a JavaScript WebRTC utility maintained by Google that abstracts away browser differences. Finally jquery.js is also needed in this application.

These libraries are linked in the index.html web page, and are used in the index.js. In the following snippet we can see the creation of the WebSocket (variable ws) in the path /call. Then, the onmessage listener of the WebSocket is used to implement the JSON signaling protocol in the client-side. Notice that there are four incoming messages to client: presenterResponse, viewerResponse, iceCandidate, and stopCommunication. Convenient actions are taken to implement each step in the communication. For example, in the function presenter the function WebRtcPeer.WebRtcPeerSendonly of kurento-utils.js is used to start a WebRTC communication. Then, WebRtcPeer.WebRtcPeerRecvonly is used in the viewer function.

var ws = new WebSocket('ws://' + location.host + '/call');

ws.onmessage = function(message) {
   var parsedMessage = JSON.parse(message.data);
   console.info('Received message: ' + message.data);

   switch (parsedMessage.id) {
   case 'presenterResponse':
      presenterResponse(parsedMessage);
      break;
   case 'viewerResponse':
      viewerResponse(parsedMessage);
      break;
   case 'iceCandidate':
       webRtcPeer.addIceCandidate(parsedMessage.candidate, function (error) {
        if (!error) return;
         console.error("Error adding candidate: " + error);
       });
       break;
   case 'stopCommunication':
      dispose();
      break;
   default:
      console.error('Unrecognized message', parsedMessage);
   }
}

function presenter() {
   if (!webRtcPeer) {
      showSpinner(video);

      var options = {
               localVideo: video,
               onicecandidate: onIceCandidate
             }
      webRtcPeer = new kurentoUtils.WebRtcPeer.WebRtcPeerSendonly(options,
         function (error) {
           if(error) {
              return console.error(error);
           }
           webRtcPeer.generateOffer(onOfferPresenter);
      });
   }
}

function viewer() {
   if (!webRtcPeer) {
      showSpinner(video);

      var options = {
               remoteVideo: video,
               onicecandidate: onIceCandidate
             }
      webRtcPeer = new kurentoUtils.WebRtcPeer.WebRtcPeerRecvonly(options,
         function (error) {
           if(error) {
              return console.error(error);
           }
          this.generateOffer(onOfferViewer);
      });
   }
}
Dependencies

This Java Spring application is implemented using Maven. The relevant part of the pom.xml is where Kurento dependencies are declared. As the following snippet shows, we need two dependencies: the Kurento Client Java dependency (kurento-client) and the JavaScript Kurento utility library (kurento-utils) for the client-side. Other client libraries are managed with webjars:

<dependencies>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-client</artifactId>
   </dependency>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-utils-js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars</groupId>
      <artifactId>webjars-locator</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>bootstrap</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>demo-console</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>adapter.js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>jquery</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>ekko-lightbox</artifactId>
   </dependency>
</dependencies>

注解

We are in active development. You can find the latest version of Kurento Java Client at Maven Central.

Kurento Java Client has a minimum requirement of Java 7. Hence, you need to include the following properties in your pom:

<maven.compiler.target>1.7</maven.compiler.target>
<maven.compiler.source>1.7</maven.compiler.source>

Node.js - One to many video call

This web application consists on one-to-many video call using WebRTC technology. In other words, it is an implementation of a video broadcasting web application.

注解

This tutorial has been configurated for using https. Follow these instructions for securing your application.

For the impatient: running this example

First of all, you should install Kurento Media Server to run this demo. Please visit the installation guide for further information.

Be sure to have installed Node.js and Bower in your system. In an Ubuntu machine, you can install both as follows:

curl -sL https://deb.nodesource.com/setup_4.x | sudo bash -
sudo apt-get install -y nodejs
sudo npm install -g bower

To launch the application, you need to clone the GitHub project where this demo is hosted, install it and run it:

git clone https://github.com/Kurento/kurento-tutorial-node.git
cd kurento-tutorial-node/kurento-one2many-call
git checkout 6.6.1
npm install
npm start

If you have problems installing any of the dependencies, please remove them and clean the npm cache, and try to install them again:

rm -r node_modules
npm cache clean

Access the application connecting to the URL https://localhost:8443/ in a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the argument ws_uri to the npm execution command, as follows:

npm start -- --ws_uri=ws://kms_host:kms_port/kurento

In this case you need to use npm version 2. To update it you can use this command:

sudo npm install npm -g
Understanding this example

There will be two types of users in this application: 1 peer sending media (let’s call it Presenter) and N peers receiving the media from the Presenter (let’s call them Viewers). Thus, the Media Pipeline is composed by 1+N interconnected WebRtcEndpoints. The following picture shows an screenshot of the Presenter’s web GUI:

One to many video call screenshot

One to many video call screenshot

To implement this behavior we have to create a Media Pipeline composed by 1+N WebRtcEndpoints. The Presenter peer sends its stream to the rest of the Viewers. Viewers are configured in receive-only mode. The implemented media pipeline is illustrated in the following picture:

One to many video call Media Pipeline

One to many video call Media Pipeline

This is a web application, and therefore it follows a client-server architecture. At the client-side, the logic is implemented in JavaScript. At the server-side we use the Kurento JavaScript Client in order to reach the Kurento Media Server. All in all, the high level architecture of this demo is three-tier. To communicate these entities two WebSockets are used. The first is created between the client browser and a Node.js application server to transport signaling messages. The second is used to communicate the Kurento JavaScript Client executing at Node.js and the Kurento Media Server. This communication is implemented by the Kurento Protocol. For further information, please see this page.

Client and application server communicate using a signaling protocol based on JSON messages over WebSocket ‘s. The normal sequence between client and server is as follows:

1. A Presenter enters in the system. There must be one and only one Presenter at any time. For that, if a Presenter has already present, an error message is sent if another user tries to become Presenter.

2. N Viewers connect to the presenter. If no Presenter is present, then an error is sent to the corresponding Viewer.

  1. Viewers can leave the communication at any time.

4. When the Presenter finishes the session each connected Viewer receives an stopCommunication message and also terminates its session.

We can draw the following sequence diagram with detailed messages between clients and server:

One to many video call signaling protocol

One to many video call signaling protocol

As you can see in the diagram, SDP and ICE candidates need to be exchanged between client and server to establish the WebRTC connection between the Kurento client and server. Specifically, the SDP negotiation connects the WebRtcPeer in the browser with the WebRtcEndpoint in the server. The complete source code of this demo can be found in GitHub.

Application Server Logic

This demo has been developed using the express framework for Node.js, but express is not a requirement for Kurento. The main script of this demo is server.js.

In order to communicate the JavaScript client and the Node application server a WebSocket is used. The incoming messages to this WebSocket (variable ws in the code) are conveniently handled to implemented the signaling protocol depicted in the figure before (i.e. messages presenter, viewer, stop, and onIceCandidate).

var ws = require('ws');

[...]

var wss = new ws.Server({
    server : server,
    path : '/one2many'
});

/*
 * Management of WebSocket messages
 */
wss.on('connection', function(ws) {

   var sessionId = nextUniqueId();
   console.log('Connection received with sessionId ' + sessionId);

    ws.on('error', function(error) {
        console.log('Connection ' + sessionId + ' error');
        stop(sessionId);
    });

    ws.on('close', function() {
        console.log('Connection ' + sessionId + ' closed');
        stop(sessionId);
    });

    ws.on('message', function(_message) {
        var message = JSON.parse(_message);
        console.log('Connection ' + sessionId + ' received message ', message);

        switch (message.id) {
        case 'presenter':
         startPresenter(sessionId, ws, message.sdpOffer, function(error, sdpAnswer) {
            if (error) {
               return ws.send(JSON.stringify({
                  id : 'presenterResponse',
                  response : 'rejected',
                  message : error
               }));
            }
            ws.send(JSON.stringify({
               id : 'presenterResponse',
               response : 'accepted',
               sdpAnswer : sdpAnswer
            }));
         });
         break;

        case 'viewer':
         startViewer(sessionId, ws, message.sdpOffer, function(error, sdpAnswer) {
            if (error) {
               return ws.send(JSON.stringify({
                  id : 'viewerResponse',
                  response : 'rejected',
                  message : error
               }));
            }

            ws.send(JSON.stringify({
               id : 'viewerResponse',
               response : 'accepted',
               sdpAnswer : sdpAnswer
            }));
         });
         break;

        case 'stop':
            stop(sessionId);
            break;

        case 'onIceCandidate':
            onIceCandidate(sessionId, message.candidate);
            break;

        default:
            ws.send(JSON.stringify({
                id : 'error',
                message : 'Invalid message ' + message
            }));
            break;
        }
    });
});

In order to control the media capabilities provided by the Kurento Media Server, we need an instance of the KurentoClient in the Node application server. In order to create this instance, we need to specify to the client library the location of the Kurento Media Server. In this example, we assume it’s located at localhost listening in port 8888.

var kurento = require('kurento-client');

var kurentoClient = null;

var argv = minimist(process.argv.slice(2), {
    default: {
        as_uri: 'https://localhost:8443/',
        ws_uri: 'ws://localhost:8888/kurento'
    }
});

[...]

function getKurentoClient(callback) {
    if (kurentoClient !== null) {
        return callback(null, kurentoClient);
    }

    kurento(argv.ws_uri, function(error, _kurentoClient) {
        if (error) {
            console.log("Could not find media server at address " + argv.ws_uri);
            return callback("Could not find media server at address" + argv.ws_uri
                    + ". Exiting with error " + error);
        }

        kurentoClient = _kurentoClient;
        callback(null, kurentoClient);
    });
}

Once the Kurento Client has been instantiated, you are ready for communicating with Kurento Media Server. Our first operation is to create a Media Pipeline, then we need to create the Media Elements and connect them. In this example, we need a WebRtcEndpoint (in send-only mode) for the presenter connected to N WebRtcEndpoint (in receive-only mode) for the viewers. These functions are called in the startPresenter and startViewer function, which is fired when the presenter and viewer message are received respectively:

function startPresenter(sessionId, ws, sdpOffer, callback) {
   clearCandidatesQueue(sessionId);

   if (presenter !== null) {
      stop(sessionId);
      return callback("Another user is currently acting as presenter. Try again later ...");
   }

   presenter = {
      id : sessionId,
      pipeline : null,
      webRtcEndpoint : null
   }

   getKurentoClient(function(error, kurentoClient) {
      if (error) {
         stop(sessionId);
         return callback(error);
      }

      if (presenter === null) {
         stop(sessionId);
         return callback(noPresenterMessage);
      }

      kurentoClient.create('MediaPipeline', function(error, pipeline) {
         if (error) {
            stop(sessionId);
            return callback(error);
         }

         if (presenter === null) {
            stop(sessionId);
            return callback(noPresenterMessage);
         }

         presenter.pipeline = pipeline;
         pipeline.create('WebRtcEndpoint', function(error, webRtcEndpoint) {
            if (error) {
               stop(sessionId);
               return callback(error);
            }

            if (presenter === null) {
               stop(sessionId);
               return callback(noPresenterMessage);
            }

            presenter.webRtcEndpoint = webRtcEndpoint;

                if (candidatesQueue[sessionId]) {
                    while(candidatesQueue[sessionId].length) {
                        var candidate = candidatesQueue[sessionId].shift();
                        webRtcEndpoint.addIceCandidate(candidate);
                    }
                }

                webRtcEndpoint.on('OnIceCandidate', function(event) {
                    var candidate = kurento.getComplexType('IceCandidate')(event.candidate);
                    ws.send(JSON.stringify({
                        id : 'iceCandidate',
                        candidate : candidate
                    }));
                });

            webRtcEndpoint.processOffer(sdpOffer, function(error, sdpAnswer) {
               if (error) {
                  stop(sessionId);
                  return callback(error);
               }

               if (presenter === null) {
                  stop(sessionId);
                  return callback(noPresenterMessage);
               }

               callback(null, sdpAnswer);
            });

                webRtcEndpoint.gatherCandidates(function(error) {
                    if (error) {
                        stop(sessionId);
                        return callback(error);
                    }
                });
            });
        });
   });
}

function startViewer(sessionId, ws, sdpOffer, callback) {
   clearCandidatesQueue(sessionId);

   if (presenter === null) {
      stop(sessionId);
      return callback(noPresenterMessage);
   }

   presenter.pipeline.create('WebRtcEndpoint', function(error, webRtcEndpoint) {
      if (error) {
         stop(sessionId);
         return callback(error);
      }
      viewers[sessionId] = {
         "webRtcEndpoint" : webRtcEndpoint,
         "ws" : ws
      }

      if (presenter === null) {
         stop(sessionId);
         return callback(noPresenterMessage);
      }

      if (candidatesQueue[sessionId]) {
         while(candidatesQueue[sessionId].length) {
            var candidate = candidatesQueue[sessionId].shift();
            webRtcEndpoint.addIceCandidate(candidate);
         }
      }

      webRtcEndpoint.on('OnIceCandidate', function(event) {
          var candidate = kurento.getComplexType('IceCandidate')(event.candidate);
          ws.send(JSON.stringify({
              id : 'iceCandidate',
              candidate : candidate
          }));
      });

      webRtcEndpoint.processOffer(sdpOffer, function(error, sdpAnswer) {
         if (error) {
            stop(sessionId);
            return callback(error);
         }
         if (presenter === null) {
            stop(sessionId);
            return callback(noPresenterMessage);
         }

         presenter.webRtcEndpoint.connect(webRtcEndpoint, function(error) {
            if (error) {
               stop(sessionId);
               return callback(error);
            }
            if (presenter === null) {
               stop(sessionId);
               return callback(noPresenterMessage);
            }

            callback(null, sdpAnswer);
              webRtcEndpoint.gatherCandidates(function(error) {
                  if (error) {
                     stop(sessionId);
                     return callback(error);
                  }
              });
          });
       });
   });
}

As of Kurento Media Server 6.0, the WebRTC negotiation is done by exchanging ICE candidates between the WebRTC peers. To implement this protocol, the webRtcEndpoint receives candidates from the client in OnIceCandidate function. These candidates are stored in a queue when the webRtcEndpoint is not available yet. Then these candidates are added to the media element by calling to the addIceCandidate method.

var candidatesQueue = {};

[...]

function onIceCandidate(sessionId, _candidate) {
    var candidate = kurento.getComplexType('IceCandidate')(_candidate);

    if (presenter && presenter.id === sessionId && presenter.webRtcEndpoint) {
        console.info('Sending presenter candidate');
        presenter.webRtcEndpoint.addIceCandidate(candidate);
    }
    else if (viewers[sessionId] && viewers[sessionId].webRtcEndpoint) {
        console.info('Sending viewer candidate');
        viewers[sessionId].webRtcEndpoint.addIceCandidate(candidate);
    }
    else {
        console.info('Queueing candidate');
        if (!candidatesQueue[sessionId]) {
            candidatesQueue[sessionId] = [];
        }
        candidatesQueue[sessionId].push(candidate);
    }
}

function clearCandidatesQueue(sessionId) {
   if (candidatesQueue[sessionId]) {
      delete candidatesQueue[sessionId];
   }
}
Client-Side Logic

Let’s move now to the client-side of the application. To call the previously created WebSocket service in the server-side, we use the JavaScript class WebSocket. We use a specific Kurento JavaScript library called kurento-utils.js to simplify the WebRTC interaction with the server. This library depends on adapter.js, which is a JavaScript WebRTC utility maintained by Google that abstracts away browser differences. Finally jquery.js is also needed in this application. These libraries are linked in the index.html web page, and are used in the index.js. In the following snippet we can see the creation of the WebSocket (variable ws) in the path /one2many. Then, the onmessage listener of the WebSocket is used to implement the JSON signaling protocol in the client-side. Notice that there are three incoming messages to client: presenterResponse, viewerResponse,``stopCommunication``, and iceCandidate. Convenient actions are taken to implement each step in the communication.

On the one hand, the function presenter uses the method WebRtcPeer.WebRtcPeerSendonly of kurento-utils.js to start a WebRTC communication in send-only mode. On the other hand, the function viewer uses the method WebRtcPeer.WebRtcPeerRecvonly of kurento-utils.js to start a WebRTC communication in receive-only mode.

var ws = new WebSocket('ws://' + location.host + '/one2many');
var webRtcPeer;

const I_CAN_START = 0;
const I_CAN_STOP = 1;
const I_AM_STARTING = 2;

[...]

ws.onmessage = function(message) {
   var parsedMessage = JSON.parse(message.data);
   console.info('Received message: ' + message.data);

   switch (parsedMessage.id) {
   case 'presenterResponse':
      presenterResponse(parsedMessage);
      break;
   case 'viewerResponse':
      viewerResponse(parsedMessage);
      break;
   case 'stopCommunication':
      dispose();
      break;
   case 'iceCandidate':
      webRtcPeer.addIceCandidate(parsedMessage.candidate)
      break;
   default:
      console.error('Unrecognized message', parsedMessage);
   }
}

function presenterResponse(message) {
   if (message.response != 'accepted') {
      var errorMsg = message.message ? message.message : 'Unknow error';
      console.warn('Call not accepted for the following reason: ' + errorMsg);
      dispose();
   } else {
      webRtcPeer.processAnswer(message.sdpAnswer);
   }
}

function viewerResponse(message) {
   if (message.response != 'accepted') {
      var errorMsg = message.message ? message.message : 'Unknow error';
      console.warn('Call not accepted for the following reason: ' + errorMsg);
      dispose();
   } else {
      webRtcPeer.processAnswer(message.sdpAnswer);
   }
}

On the one hand, the function presenter uses the method WebRtcPeer.WebRtcPeerSendonly of kurento-utils.js to start a WebRTC communication in send-only mode. On the other hand, the function viewer uses the method WebRtcPeer.WebRtcPeerRecvonly of kurento-utils.js to start a WebRTC communication in receive-only mode.

function presenter() {
   if (!webRtcPeer) {
      showSpinner(video);

      var options = {
         localVideo: video,
         onicecandidate : onIceCandidate
       }

      webRtcPeer = kurentoUtils.WebRtcPeer.WebRtcPeerSendonly(options, function(error) {
         if(error) return onError(error);

         this.generateOffer(onOfferPresenter);
      });
   }
}

function onOfferPresenter(error, offerSdp) {
   if (error) return onError(error);

   var message = {
      id : 'presenter',
      sdpOffer : offerSdp
   };
   sendMessage(message);
}

function viewer() {
   if (!webRtcPeer) {
      showSpinner(video);

      var options = {
         remoteVideo: video,
         onicecandidate : onIceCandidate
      }

      webRtcPeer = kurentoUtils.WebRtcPeer.WebRtcPeerRecvonly(options, function(error) {
         if(error) return onError(error);

         this.generateOffer(onOfferViewer);
      });
   }
}

function onOfferViewer(error, offerSdp) {
   if (error) return onError(error)

   var message = {
      id : 'viewer',
      sdpOffer : offerSdp
   }
   sendMessage(message);
}
Dependencies

Server-side dependencies of this demo are managed using npm. Our main dependency is the Kurento Client JavaScript (kurento-client). The relevant part of the package.json file for managing this dependency is:

"dependencies": {
   [...]
   "kurento-client" : "6.6.0"
}

At the client side, dependencies are managed using Bower. Take a look to the bower.json file and pay attention to the following section:

"dependencies": {
   [...]
   "kurento-utils" : "6.6.2"
}

注解

We are in active development. You can find the latest version of Kurento JavaScript Client at npm and Bower.

WebRTC one-to-one video call

This web application is a videophone (call one to one) based on WebRTC.

Java - One to one video call

This web application consists on a one-to-one video call using WebRTC technology. In other words, this application provides a simple video softphone.

注解

This tutorial has been configured to use https. Follow the instructions to secure your application.

For the impatient: running this example

First of all, you should install Kurento Media Server to run this demo. Please visit the installation guide for further information.

To launch the application, you need to clone the GitHub project where this demo is hosted, and then run the main class:

git clone https://github.com/Kurento/kurento-tutorial-java.git
cd kurento-tutorial-java/kurento-one2one-call
git checkout 6.6.2
mvn compile exec:java

The web application starts on port 8443 in the localhost by default. Therefore, open the URL https://localhost:8443/ in a WebRTC compliant browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the flag kms.url to the JVM executing the demo. As we’ll be using maven, you should execute the following command

mvn compile exec:java -Dkms.url=ws://kms_host:kms_port/kurento
Understanding this example

The following picture shows an screenshot of this demo running in a web browser:

One to one video call screenshot

One to one video call screenshot

The interface of the application (an HTML web page) is composed by two HTML5 video tags: one for the local stream and other for the remote peer stream). If two users, A and B, are using the application, the media flow goes this way: The video camera stream of user A is sent to the Kurento Media Server, which sends it to user B. In the same way, B sends to Kurento Media Server, which forwards it to A. This means that KMS is providing a B2B (back-to-back) call service.

To implement this behavior, create sa Media Pipeline composed by two WebRtC endpoints connected in B2B. The implemented media pipeline is illustrated in the following picture:

One to one video call media pipeline

One to one video call Media Pipeline

The client and the server communicate through a signaling protocol based on JSON messages over WebSocket ‘s. The normal sequence between client and server would be as follows:

  1. User A is registered in the server with his name
  2. User B is registered in the server with her name
  3. User A wants to call to User B
  4. User B accepts the incoming call
  5. The communication is established and media is flowing between User A and User B
  6. One of the users finishes the video communication

The detailed message flow in a call are shown in the picture below:

One to one video call signaling protocol

One to many one call signaling protocol

As you can see in the diagram, SDP and ICE candidates need to be interchanged between client and server to establish the WebRTC connection between the Kurento client and server. Specifically, the SDP negotiation connects the WebRtcPeer in the browser with the WebRtcEndpoint in the server.

The following sections describe in detail the server-side, the client-side, and how to run the demo. The complete source code of this demo can be found in GitHub.

Application Server Logic

This demo has been developed using Java in the server-side, based on the Spring Boot framework, which embeds a Tomcat web server within the generated maven artifact, and thus simplifies the development and deployment process.

注解

You can use whatever Java server side technology you prefer to build web applications with Kurento. For example, a pure Java EE application, SIP Servlets, Play, Vertex, etc. We have choose Spring Boot for convenience.

In the following figure you can see a class diagram of the server side code:

Server-side class diagram of the one to one video call app

Server-side class diagram of the one to one video call app

The main class of this demo is named One2OneCallApp. As you can see, the KurentoClient is instantiated in this class as a Spring Bean.

@EnableWebSocket
@SpringBootApplication
public class One2OneCallApp implements WebSocketConfigurer {

   @Bean
   public CallHandler callHandler() {
      return new CallHandler();
   }

   @Bean
   public UserRegistry registry() {
      return new UserRegistry();
   }

   @Bean
   public KurentoClient kurentoClient() {
      return KurentoClient.create();
   }

   public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
      registry.addHandler(callHandler(), "/call");
   }

   public static void main(String[] args) throws Exception {
      new SpringApplication(One2OneCallApp.class).run(args);
   }

}

This web application follows a Single Page Application architecture (SPA), and uses a WebSocket to communicate client with server by means of requests and responses. Specifically, the main app class implements the interface WebSocketConfigurer to register a WebSocketHanlder to process WebSocket requests in the path /call.

CallHandler class implements TextWebSocketHandler to handle text WebSocket requests. The central piece of this class is the method handleTextMessage. This method implements the actions for requests, returning responses through the WebSocket. In other words, it implements the server part of the signaling protocol depicted in the previous sequence diagram.

In the designed protocol there are five different kind of incoming messages to the application server: register, call, incomingCallResponse, onIceCandidate and stop. These messages are treated in the switch clause, taking the proper steps in each case.

public class CallHandler extends TextWebSocketHandler {

   private static final Logger log = LoggerFactory.getLogger(CallHandler.class);
   private static final Gson gson = new GsonBuilder().create();

   private final ConcurrentHashMap<String, CallMediaPipeline> pipelines = new ConcurrentHashMap<String, CallMediaPipeline>();

   @Autowired
   private KurentoClient kurento;

   @Autowired
   private UserRegistry registry;

   @Override
   public void handleTextMessage(WebSocketSession session, TextMessage message) throws Exception {
      JsonObject jsonMessage = gson.fromJson(message.getPayload(), JsonObject.class);
      UserSession user = registry.getBySession(session);

      if (user != null) {
         log.debug("Incoming message from user '{}': {}", user.getName(), jsonMessage);
      } else {
         log.debug("Incoming message from new user: {}", jsonMessage);
      }

      switch (jsonMessage.get("id").getAsString()) {
      case "register":
         try {
            register(session, jsonMessage);
         } catch (Throwable t) {
            handleErrorResponse(t, session, "registerResponse");
         }
         break;
      case "call":
         try {
            call(user, jsonMessage);
         } catch (Throwable t) {
            handleErrorResponse(t, session, "callResponse");
         }
         break;
      case "incomingCallResponse":
         incomingCallResponse(user, jsonMessage);
         break;
      case "onIceCandidate": {
         JsonObject candidate = jsonMessage.get("candidate").getAsJsonObject();
         if (user != null) {
            IceCandidate cand = new IceCandidate(candidate.get("candidate").getAsString(),
                  candidate.get("sdpMid").getAsString(), candidate.get("sdpMLineIndex").getAsInt());
            user.addCandidate(cand);
         }
         break;
      }
      case "stop":
         stop(session);
         break;
      default:
         break;
      }
   }

   private void handleErrorResponse(Throwable t, WebSocketSession session,
         String responseId) throws IOException {
      stop(session);
      log.error(t.getMessage(), t);
      JsonObject response = new JsonObject();
      response.addProperty("id", responseId);
      response.addProperty("response", "rejected");
      response.addProperty("message", t.getMessage());
      session.sendMessage(new TextMessage(response.toString()));
   }

   private void register(WebSocketSession session, JsonObject jsonMessage) throws IOException {
      ...
   }

   private void call(UserSession caller, JsonObject jsonMessage) throws IOException {
      ...
   }

   private void incomingCallResponse(final UserSession callee, JsonObject jsonMessage) throws IOException {
      ...
   }

   public void stop(WebSocketSession session) throws IOException {
      ...
   }

   @Override
   public void afterConnectionClosed(WebSocketSession session, CloseStatus status) throws Exception {
      stop(session);
      registry.removeBySession(session);
   }

}

In the following snippet, we can see the register method. Basically, it obtains the name attribute from register message and check if there are a registered user with that name. If not, the new user is registered and an acceptance message is sent to it.

private void register(WebSocketSession session, JsonObject jsonMessage) throws IOException {
   String name = jsonMessage.getAsJsonPrimitive("name").getAsString();

   UserSession caller = new UserSession(session, name);
   String responseMsg = "accepted";
   if (name.isEmpty()) {
      responseMsg = "rejected: empty user name";
   } else if (registry.exists(name)) {
      responseMsg = "rejected: user '" + name + "' already registered";
   } else {
      registry.register(caller);
   }

   JsonObject response = new JsonObject();
   response.addProperty("id", "resgisterResponse");
   response.addProperty("response", responseMsg);
   caller.sendMessage(response);
}

In the call method, the server checks if there is a registered user with the name specified in to message attribute, and sends an incomingCall message. If there is no user with that name, a callResponse message is sent to caller rejecting the call.

private void call(UserSession caller, JsonObject jsonMessage) throws IOException {
   String to = jsonMessage.get("to").getAsString();
   String from = jsonMessage.get("from").getAsString();
   JsonObject response = new JsonObject();

   if (registry.exists(to)) {
      UserSession callee = registry.getByName(to);
      caller.setSdpOffer(jsonMessage.getAsJsonPrimitive("sdpOffer").getAsString());
      caller.setCallingTo(to);

      response.addProperty("id", "incomingCall");
      response.addProperty("from", from);

      callee.sendMessage(response);
      callee.setCallingFrom(from);
   } else {
      response.addProperty("id", "callResponse");
      response.addProperty("response", "rejected: user '" + to + "' is not registered");

      caller.sendMessage(response);
   }
}

The stop method ends the video call. It can be called both by caller and callee in the communication. The result is that both peers release the Media Pipeline and ends the video communication:

public void stop(WebSocketSession session) throws IOException {
   String sessionId = session.getId();
   if (pipelines.containsKey(sessionId)) {
      pipelines.get(sessionId).release();
      CallMediaPipeline pipeline = pipelines.remove(sessionId);
      pipeline.release();

      // Both users can stop the communication. A 'stopCommunication'
      // message will be sent to the other peer.
      UserSession stopperUser = registry.getBySession(session);
      if (stopperUser != null) {
         UserSession stoppedUser = (stopperUser.getCallingFrom() != null)
               ? registry.getByName(stopperUser.getCallingFrom())
               : stopperUser.getCallingTo() != null
                     ? registry.getByName(stopperUser.getCallingTo())
                     : null;

         if (stoppedUser != null) {
            JsonObject message = new JsonObject();
            message.addProperty("id", "stopCommunication");
            stoppedUser.sendMessage(message);
            stoppedUser.clear();
         }
         stopperUser.clear();
      }

   }
}

In the incomingCallResponse method, if the callee user accepts the call, it is established and the media elements are created to connect the caller with the callee in a B2B manner. Basically, the server creates a CallMediaPipeline object, to encapsulate the media pipeline creation and management. Then, this object is used to negotiate media interchange with user’s browsers.

The negotiation between WebRTC peer in the browser and WebRtcEndpoint in Kurento Media Server is made by means of SDP generation at the client (offer) and SDP generation at the server (answer). The SDP answers are generated with the Kurento Java Client inside the class CallMediaPipeline (as we see in a moment). The methods used to generate SDP are generateSdpAnswerForCallee(calleeSdpOffer) and generateSdpAnswerForCaller(callerSdpOffer):

private void incomingCallResponse(final UserSession callee, JsonObject jsonMessage) throws IOException {
   String callResponse = jsonMessage.get("callResponse").getAsString();
   String from = jsonMessage.get("from").getAsString();
   final UserSession calleer = registry.getByName(from);
   String to = calleer.getCallingTo();

   if ("accept".equals(callResponse)) {
      log.debug("Accepted call from '{}' to '{}'", from, to);

      CallMediaPipeline pipeline = null;
      try {
         pipeline = new CallMediaPipeline(kurento);
         pipelines.put(calleer.getSessionId(), pipeline);
         pipelines.put(callee.getSessionId(), pipeline);

         String calleeSdpOffer = jsonMessage.get("sdpOffer").getAsString();
         callee.setWebRtcEndpoint(pipeline.getCalleeWebRtcEP());
         pipeline.getCalleeWebRtcEP().addIceCandidateFoundListener(new EventListener<IceCandidateFoundEvent>() {
            @Override
            public void onEvent(IceCandidateFoundEvent event) {
               JsonObject response = new JsonObject();
               response.addProperty("id", "iceCandidate");
               response.add("candidate", JsonUtils.toJsonObject(event.getCandidate()));
               try {
                  synchronized (callee.getSession()) {
                     callee.getSession().sendMessage(new TextMessage(response.toString()));
                  }
               } catch (IOException e) {
                  log.debug(e.getMessage());
               }
            }
         });

         String calleeSdpAnswer = pipeline.generateSdpAnswerForCallee(calleeSdpOffer);
         String callerSdpOffer = registry.getByName(from).getSdpOffer();
         calleer.setWebRtcEndpoint(pipeline.getCallerWebRtcEP());
         pipeline.getCallerWebRtcEP().addIceCandidateFoundListener(new EventListener<IceCandidateFoundEvent>() {

            @Override
            public void onEvent(IceCandidateFoundEvent event) {
               JsonObject response = new JsonObject();
               response.addProperty("id", "iceCandidate");
               response.add("candidate", JsonUtils.toJsonObject(event.getCandidate()));
               try {
                  synchronized (calleer.getSession()) {
                     calleer.getSession().sendMessage(new TextMessage(response.toString()));
                  }
               } catch (IOException e) {
                  log.debug(e.getMessage());
               }
            }
         });

         String callerSdpAnswer = pipeline.generateSdpAnswerForCaller(callerSdpOffer);

         JsonObject startCommunication = new JsonObject();
         startCommunication.addProperty("id", "startCommunication");
         startCommunication.addProperty("sdpAnswer", calleeSdpAnswer);

         synchronized (callee) {
            callee.sendMessage(startCommunication);
         }

         pipeline.getCalleeWebRtcEP().gatherCandidates();

         JsonObject response = new JsonObject();
         response.addProperty("id", "callResponse");
         response.addProperty("response", "accepted");
         response.addProperty("sdpAnswer", callerSdpAnswer);

         synchronized (calleer) {
            calleer.sendMessage(response);
         }

         pipeline.getCallerWebRtcEP().gatherCandidates();

      } catch (Throwable t) {
         log.error(t.getMessage(), t);

         if (pipeline != null) {
            pipeline.release();
         }

         pipelines.remove(calleer.getSessionId());
         pipelines.remove(callee.getSessionId());

         JsonObject response = new JsonObject();
         response.addProperty("id", "callResponse");
         response.addProperty("response", "rejected");
         calleer.sendMessage(response);

         response = new JsonObject();
         response.addProperty("id", "stopCommunication");
         callee.sendMessage(response);
      }

   } else {
      JsonObject response = new JsonObject();
      response.addProperty("id", "callResponse");
      response.addProperty("response", "rejected");
      calleer.sendMessage(response);
   }
}

The media logic in this demo is implemented in the class CallMediaPipeline. As you can see, the media pipeline of this demo is quite simple: two WebRtcEndpoint elements directly interconnected. Please take note that the WebRtcEndpoints need to be connected twice, one for each media direction.

public class CallMediaPipeline {

   private MediaPipeline pipeline;
   private WebRtcEndpoint callerWebRtcEP;
   private WebRtcEndpoint calleeWebRtcEP;

   public CallMediaPipeline(KurentoClient kurento) {
      try {
         this.pipeline = kurento.createMediaPipeline();
         this.callerWebRtcEP = new WebRtcEndpoint.Builder(pipeline).build();
         this.calleeWebRtcEP = new WebRtcEndpoint.Builder(pipeline).build();

         this.callerWebRtcEP.connect(this.calleeWebRtcEP);
         this.calleeWebRtcEP.connect(this.callerWebRtcEP);
      } catch (Throwable t) {
         if (this.pipeline != null) {
            pipeline.release();
         }
      }
   }

   public String generateSdpAnswerForCaller(String sdpOffer) {
      return callerWebRtcEP.processOffer(sdpOffer);
   }

   public String generateSdpAnswerForCallee(String sdpOffer) {
      return calleeWebRtcEP.processOffer(sdpOffer);
   }

   public void release() {
      if (pipeline != null) {
         pipeline.release();
      }
   }

   public WebRtcEndpoint getCallerWebRtcEP() {
      return callerWebRtcEP;
   }

   public WebRtcEndpoint getCalleeWebRtcEP() {
      return calleeWebRtcEP;
   }

}

In this class we can see the implementation of methods generateSdpAnswerForCaller and generateSdpAnswerForCallee. These methods delegate to WebRtc endpoints to create the appropriate answer.

Client-Side

Let’s move now to the client-side of the application. To call the previously created WebSocket service in the server-side, we use the JavaScript class WebSocket. We use a specific Kurento JavaScript library called kurento-utils.js to simplify the WebRTC interaction with the server. This library depends on adapter.js, which is a JavaScript WebRTC utility maintained by Google that abstracts away browser differences. Finally jquery.js is also needed in this application.

These libraries are linked in the index.html web page, and are used in the index.js.

In the following snippet we can see the creation of the WebSocket (variable ws) in the path /call. Then, the onmessage listener of the WebSocket is used to implement the JSON signaling protocol in the client-side. Notice that there are five incoming messages to client: resgisterResponse, callResponse, incomingCall, iceCandidate and startCommunication. Convenient actions are taken to implement each step in the communication. For example, in functions call and incomingCall (for caller and callee respectively), the function WebRtcPeer.WebRtcPeerSendrecv of kurento-utils.js is used to start a WebRTC communication.

 var ws = new WebSocket('ws://' + location.host + '/call');

ws.onmessage = function(message) {
   var parsedMessage = JSON.parse(message.data);
   console.info('Received message: ' + message.data);

   switch (parsedMessage.id) {
   case 'resgisterResponse':
      resgisterResponse(parsedMessage);
      break;
   case 'callResponse':
      callResponse(parsedMessage);
      break;
   case 'incomingCall':
      incomingCall(parsedMessage);
      break;
   case 'startCommunication':
      startCommunication(parsedMessage);
      break;
   case 'stopCommunication':
      console.info("Communication ended by remote peer");
      stop(true);
      break;
   case 'iceCandidate':
       webRtcPeer.addIceCandidate(parsedMessage.candidate, function (error) {
        if (!error) return;
         console.error("Error adding candidate: " + error);
       });
       break;
   default:
      console.error('Unrecognized message', parsedMessage);
   }
}

function incomingCall(message) {
   //If bussy just reject without disturbing user
   if (callState != NO_CALL) {
      var response = {
         id : 'incomingCallResponse',
         from : message.from,
         callResponse : 'reject',
         message : 'bussy'
      };
      return sendMessage(response);
   }

   setCallState(PROCESSING_CALL);
   if (confirm('User ' + message.from
         + ' is calling you. Do you accept the call?')) {
      showSpinner(videoInput, videoOutput);

      from = message.from;
      var options = {
               localVideo: videoInput,
               remoteVideo: videoOutput,
               onicecandidate: onIceCandidate,
               onerror: onError
             }
       webRtcPeer = new kurentoUtils.WebRtcPeer.WebRtcPeerSendrecv(options,
         function (error) {
           if(error) {
              return console.error(error);
           }
           webRtcPeer.generateOffer (onOfferIncomingCall);
         });

   } else {
      var response = {
         id : 'incomingCallResponse',
         from : message.from,
         callResponse : 'reject',
         message : 'user declined'
      };
      sendMessage(response);
      stop();
   }
}

function call() {
   if (document.getElementById('peer').value == '') {
      window.alert("You must specify the peer name");
      return;
   }
   setCallState(PROCESSING_CALL);
   showSpinner(videoInput, videoOutput);

   var options = {
            localVideo: videoInput,
            remoteVideo: videoOutput,
            onicecandidate: onIceCandidate,
            onerror: onError
          }
   webRtcPeer = new kurentoUtils.WebRtcPeer.WebRtcPeerSendrecv(options,
      function (error) {
        if(error) {
           return console.error(error);
        }
        webRtcPeer.generateOffer (onOfferCall);
   });
}
Dependencies

This Java Spring application is implemented using Maven. The relevant part of the pom.xml is where Kurento dependencies are declared. As the following snippet shows, we need two dependencies: the Kurento Client Java dependency (kurento-client) and the JavaScript Kurento utility library (kurento-utils) for the client-side. Other client libraries are managed with webjars:

<dependencies>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-client</artifactId>
   </dependency>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-utils-js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars</groupId>
      <artifactId>webjars-locator</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>bootstrap</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>demo-console</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>draggabilly</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>adapter.js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>jquery</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>ekko-lightbox</artifactId>
   </dependency>
</dependencies>

注解

We are in active development. You can find the latest version of Kurento Java Client at Maven Central.

Kurento Java Client has a minimum requirement of Java 7. Hence, you need to include the following properties in your pom:

<maven.compiler.target>1.7</maven.compiler.target>
<maven.compiler.source>1.7</maven.compiler.source>

Node.js - One to one video call

This web application consists on a one-to-one video call using WebRTC technology. In other words, this application provides a simple video softphone.

注解

This tutorial has been configurated for using https. Follow these instructions for securing your application.

For the impatient: running this example

First of all, you should install Kurento Media Server to run this demo. Please visit the installation guide for further information.

Be sure to have installed Node.js and Bower in your system. In an Ubuntu machine, you can install both as follows:

curl -sL https://deb.nodesource.com/setup_4.x | sudo bash -
sudo apt-get install -y nodejs
sudo npm install -g bower

To launch the application, you need to clone the GitHub project where this demo is hosted, install it and run it:

git clone https://github.com/Kurento/kurento-tutorial-node.git
cd kurento-tutorial-node/kurento-one2one-call
git checkout 6.6.1
npm install
npm start

If you have problems installing any of the dependencies, please remove them and clean the npm cache, and try to install them again:

rm -r node_modules
npm cache clean

Access the application connecting to the URL https://localhost:8443/ in a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the argument ws_uri to the npm execution command, as follows:

npm start -- --ws_uri=ws://kms_host:kms_port/kurento

In this case you need to use npm version 2. To update it you can use this command:

sudo npm install npm -g
Understanding this example

The following picture shows an screenshot of this demo running in a web browser:

One to one video call screenshot

One to one video call screenshot

The interface of the application (an HTML web page) is composed by two HTML5 video tags: one for the local stream and other for the remote peer stream). If two users, A and B, are using the application, the media flow goes this way: The video camera stream of user A is sent to the Kurento Media Server, which sends it to user B. In the same way, B sends to Kurento Media Server, which forwards it to A. This means that KMS is providing a B2B (back-to-back) call service.

To implement this behavior create a Media Pipeline composed by two WebRtC endpoints connected in B2B. The implemented media pipeline is illustrated in the following picture:

One to one video call media pipeline

One to one video call Media Pipeline

The client and the server communicate through a signaling protocol based on JSON messages over WebSocket ‘s. The normal sequence between client and application server logic is as follows:

  1. User A is registered in the application server with his name
  2. User B is registered in the application server with her name
  3. User A issues a call to User B
  4. User B accepts the incoming call
  5. The communication is established and media flows between User A and User B
  6. One of the users finishes the video communication

The detailed message flow in a call are shown in the picture below:

One to one video call signaling protocol

One to many one call signaling protocol

As you can see in the diagram, SDP and ICE candidates need to be exchanged between client and server to establish the WebRTC connection between the Kurento client and server. Specifically, the SDP negotiation connects the WebRtcPeer in the browser with the WebRtcEndpoint in the server. The complete source code of this demo can be found in GitHub.

Application Server Logic

This demo has been developed using the express framework for Node.js, but express is not a requirement for Kurento. The main script of this demo is server.js.

In order to communicate the JavaScript client and the Node application server a WebSocket is used. The incoming messages to this WebSocket (variable ws in the code) are conveniently handled to implemented the signaling protocol depicted in the figure before (i.e. messages register, call, incomingCallResponse, stop, and onIceCandidate).

var ws = require('ws');

[...]

var wss = new ws.Server({
    server : server,
    path : '/one2one'
});

wss.on('connection', function(ws) {
    var sessionId = nextUniqueId();
    console.log('Connection received with sessionId ' + sessionId);

    ws.on('error', function(error) {
        console.log('Connection ' + sessionId + ' error');
        stop(sessionId);
    });

    ws.on('close', function() {
        console.log('Connection ' + sessionId + ' closed');
        stop(sessionId);
        userRegistry.unregister(sessionId);
    });

    ws.on('message', function(_message) {
        var message = JSON.parse(_message);
        console.log('Connection ' + sessionId + ' received message ', message);

        switch (message.id) {
        case 'register':
            register(sessionId, message.name, ws);
            break;

        case 'call':
            call(sessionId, message.to, message.from, message.sdpOffer);
            break;

        case 'incomingCallResponse':
            incomingCallResponse(sessionId, message.from, message.callResponse, message.sdpOffer, ws);
            break;

        case 'stop':
            stop(sessionId);
            break;

        case 'onIceCandidate':
            onIceCandidate(sessionId, message.candidate);
            break;

        default:
            ws.send(JSON.stringify({
                id : 'error',
                message : 'Invalid message ' + message
            }));
            break;
        }

    });
});

In order to perform a call, each user (the caller and the callee) must be register in the system. For this reason, in the server-side there is a class named UserRegistry to store and locate users. Then, the register message fires the execution of the following function:

// Represents registrar of users
function UserRegistry() {
    this.usersById = {};
    this.usersByName = {};
}

UserRegistry.prototype.register = function(user) {
    this.usersById[user.id] = user;
    this.usersByName[user.name] = user;
}

UserRegistry.prototype.unregister = function(id) {
    var user = this.getById(id);
    if (user) delete this.usersById[id]
    if (user && this.getByName(user.name)) delete this.usersByName[user.name];
}

UserRegistry.prototype.getById = function(id) {
    return this.usersById[id];
}

UserRegistry.prototype.getByName = function(name) {
    return this.usersByName[name];
}

UserRegistry.prototype.removeById = function(id) {
    var userSession = this.usersById[id];
    if (!userSession) return;
    delete this.usersById[id];
    delete this.usersByName[userSession.name];
}

function register(id, name, ws, callback) {
    function onError(error) {
        ws.send(JSON.stringify({id:'registerResponse', response : 'rejected ', message: error}));
    }

    if (!name) {
        return onError("empty user name");
    }

    if (userRegistry.getByName(name)) {
        return onError("User " + name + " is already registered");
    }

    userRegistry.register(new UserSession(id, name, ws));
    try {
        ws.send(JSON.stringify({id: 'registerResponse', response: 'accepted'}));
    } catch(exception) {
        onError(exception);
    }
}

In order to control the media capabilities provided by the Kurento Media Server, we need an instance of the KurentoClient in the Node application server. In order to create this instance, we need to specify to the client library the location of the Kurento Media Server. In this example, we assume it’s located at localhost listening in port 8888.

var kurento = require('kurento-client');

var kurentoClient = null;

var argv = minimist(process.argv.slice(2), {
    default: {
        as_uri: 'https://localhost:8443/',
        ws_uri: 'ws://localhost:8888/kurento'
    }
});

[...]

function getKurentoClient(callback) {
    if (kurentoClient !== null) {
        return callback(null, kurentoClient);
    }

    kurento(argv.ws_uri, function(error, _kurentoClient) {
        if (error) {
            console.log("Could not find media server at address " + argv.ws_uri);
            return callback("Could not find media server at address" + argv.ws_uri
                    + ". Exiting with error " + error);
        }

        kurentoClient = _kurentoClient;
        callback(null, kurentoClient);
    });
}

Once the Kurento Client has been instantiated, you are ready for communicating with Kurento Media Server. Our first operation is to create a Media Pipeline, then we need to create the Media Elements and connect them. In this example, we need two WebRtcEndpoints, i.e. one peer caller and other one for the callee. This media logic is implemented in the class CallMediaPipeline. Note that the WebRtcEndpoints need to be connected twice, one for each media direction. This object is created in the function incomingCallResponse which is fired in the callee peer, after the caller executes the function call:

function call(callerId, to, from, sdpOffer) {
    clearCandidatesQueue(callerId);

    var caller = userRegistry.getById(callerId);
    var rejectCause = 'User ' + to + ' is not registered';
    if (userRegistry.getByName(to)) {
        var callee = userRegistry.getByName(to);
        caller.sdpOffer = sdpOffer
        callee.peer = from;
        caller.peer = to;
        var message = {
            id: 'incomingCall',
            from: from
        };
        try{
            return callee.sendMessage(message);
        } catch(exception) {
            rejectCause = "Error " + exception;
        }
    }
    var message  = {
        id: 'callResponse',
        response: 'rejected: ',
        message: rejectCause
    };
    caller.sendMessage(message);
}

function incomingCallResponse(calleeId, from, callResponse, calleeSdp, ws) {
    clearCandidatesQueue(calleeId);

    function onError(callerReason, calleeReason) {
        if (pipeline) pipeline.release();
        if (caller) {
            var callerMessage = {
                id: 'callResponse',
                response: 'rejected'
            }
            if (callerReason) callerMessage.message = callerReason;
            caller.sendMessage(callerMessage);
        }

        var calleeMessage = {
            id: 'stopCommunication'
        };
        if (calleeReason) calleeMessage.message = calleeReason;
        callee.sendMessage(calleeMessage);
    }

    var callee = userRegistry.getById(calleeId);
    if (!from || !userRegistry.getByName(from)) {
        return onError(null, 'unknown from = ' + from);
    }
    var caller = userRegistry.getByName(from);

    if (callResponse === 'accept') {
        var pipeline = new CallMediaPipeline();
        pipelines[caller.id] = pipeline;
        pipelines[callee.id] = pipeline;

        pipeline.createPipeline(caller.id, callee.id, ws, function(error) {
            if (error) {
                return onError(error, error);
            }

            pipeline.generateSdpAnswer(caller.id, caller.sdpOffer, function(error, callerSdpAnswer) {
                if (error) {
                    return onError(error, error);
                }

                pipeline.generateSdpAnswer(callee.id, calleeSdp, function(error, calleeSdpAnswer) {
                    if (error) {
                        return onError(error, error);
                    }

                    var message = {
                        id: 'startCommunication',
                        sdpAnswer: calleeSdpAnswer
                    };
                    callee.sendMessage(message);

                    message = {
                        id: 'callResponse',
                        response : 'accepted',
                        sdpAnswer: callerSdpAnswer
                    };
                    caller.sendMessage(message);
                });
            });
        });
    } else {
        var decline = {
            id: 'callResponse',
            response: 'rejected',
            message: 'user declined'
        };
        caller.sendMessage(decline);
    }
}

As of Kurento Media Server 6.0, the WebRTC negotiation is done by exchanging ICE candidates between the WebRTC peers. To implement this protocol, the webRtcEndpoint receives candidates from the client in OnIceCandidate function. These candidates are stored in a queue when the webRtcEndpoint is not available yet. Then these candidates are added to the media element by calling to the addIceCandidate method.

var candidatesQueue = {};

[...]

function onIceCandidate(sessionId, _candidate) {
    var candidate = kurento.getComplexType('IceCandidate')(_candidate);
    var user = userRegistry.getById(sessionId);

    if (pipelines[user.id] && pipelines[user.id].webRtcEndpoint && pipelines[user.id].webRtcEndpoint[user.id]) {
        var webRtcEndpoint = pipelines[user.id].webRtcEndpoint[user.id];
        webRtcEndpoint.addIceCandidate(candidate);
    }
    else {
        if (!candidatesQueue[user.id]) {
            candidatesQueue[user.id] = [];
        }
        candidatesQueue[sessionId].push(candidate);
    }
}

function clearCandidatesQueue(sessionId) {
    if (candidatesQueue[sessionId]) {
        delete candidatesQueue[sessionId];
    }
}
Client-Side Logic

Let’s move now to the client-side of the application. To call the previously created WebSocket service in the server-side, we use the JavaScript class WebSocket. We use a specific Kurento JavaScript library called kurento-utils.js to simplify the WebRTC interaction with the server. This library depends on adapter.js, which is a JavaScript WebRTC utility maintained by Google that abstracts away browser differences. Finally jquery.js is also needed in this application. These libraries are linked in the index.html web page, and are used in the index.js. In the following snippet we can see the creation of the WebSocket (variable ws) in the path /one2one. Then, the onmessage listener of the WebSocket is used to implement the JSON signaling protocol in the client-side. Notice that there are three incoming messages to client: startResponse, error, and iceCandidate. Convenient actions are taken to implement each step in the communication. For example, in functions start the function WebRtcPeer.WebRtcPeerSendrecv of kurento-utils.js is used to start a WebRTC communication.

var ws = new WebSocket('ws://' + location.host + '/one2one');
var webRtcPeer;

[...]

ws.onmessage = function(message) {
   var parsedMessage = JSON.parse(message.data);
   console.info('Received message: ' + message.data);

   switch (parsedMessage.id) {
   case 'registerResponse':
      resgisterResponse(parsedMessage);
      break;
   case 'callResponse':
      callResponse(parsedMessage);
      break;
   case 'incomingCall':
      incomingCall(parsedMessage);
      break;
   case 'startCommunication':
      startCommunication(parsedMessage);
      break;
   case 'stopCommunication':
      console.info("Communication ended by remote peer");
      stop(true);
      break;
   case 'iceCandidate':
      webRtcPeer.addIceCandidate(parsedMessage.candidate)
      break;
   default:
      console.error('Unrecognized message', parsedMessage);
   }
}

On the one hand, the function call is executed in the caller client-side, using the method WebRtcPeer.WebRtcPeerSendrecv of kurento-utils.js to start a WebRTC communication in duplex mode. On the other hand, the function incomingCall in the callee client-side uses also the method WebRtcPeer.WebRtcPeerSendrecv of kurento-utils.js to complete the WebRTC call.

function call() {
   if (document.getElementById('peer').value == '') {
      window.alert("You must specify the peer name");
      return;
   }

   setCallState(PROCESSING_CALL);

   showSpinner(videoInput, videoOutput);

   var options = {
      localVideo : videoInput,
      remoteVideo : videoOutput,
      onicecandidate : onIceCandidate
   }

   webRtcPeer = kurentoUtils.WebRtcPeer.WebRtcPeerSendrecv(options, function(
         error) {
      if (error) {
         console.error(error);
         setCallState(NO_CALL);
      }

      this.generateOffer(function(error, offerSdp) {
         if (error) {
            console.error(error);
            setCallState(NO_CALL);
         }
         var message = {
            id : 'call',
            from : document.getElementById('name').value,
            to : document.getElementById('peer').value,
            sdpOffer : offerSdp
         };
         sendMessage(message);
      });
   });
}

function incomingCall(message) {
   // If bussy just reject without disturbing user
   if (callState != NO_CALL) {
      var response = {
         id : 'incomingCallResponse',
         from : message.from,
         callResponse : 'reject',
         message : 'bussy'

      };
      return sendMessage(response);
   }

   setCallState(PROCESSING_CALL);
   if (confirm('User ' + message.from
         + ' is calling you. Do you accept the call?')) {
      showSpinner(videoInput, videoOutput);

      var options = {
         localVideo : videoInput,
         remoteVideo : videoOutput,
         onicecandidate : onIceCandidate
      }

      webRtcPeer = kurentoUtils.WebRtcPeer.WebRtcPeerSendrecv(options,
            function(error) {
               if (error) {
                  console.error(error);
                  setCallState(NO_CALL);
               }

               this.generateOffer(function(error, offerSdp) {
                  if (error) {
                     console.error(error);
                     setCallState(NO_CALL);
                  }
                  var response = {
                     id : 'incomingCallResponse',
                     from : message.from,
                     callResponse : 'accept',
                     sdpOffer : offerSdp
                  };
                  sendMessage(response);
               });
            });

   } else {
      var response = {
         id : 'incomingCallResponse',
         from : message.from,
         callResponse : 'reject',
         message : 'user declined'
      };
      sendMessage(response);
      stop(true);
   }
}
Dependencies

Server-side dependencies of this demo are managed using npm. Our main dependency is the Kurento Client JavaScript (kurento-client). The relevant part of the package.json file for managing this dependency is:

"dependencies": {
   [...]
   "kurento-client" : "6.6.0"
}

At the client side, dependencies are managed using Bower. Take a look to the bower.json file and pay attention to the following section:

"dependencies": {
   [...]
   "kurento-utils" : "6.6.2"
}

注解

We are in active development. You can find the latest version of Kurento JavaScript Client at npm and Bower.

WebRTC one-to-one video call with recording and filtering

This is an enhanced version of the the one-to-one application with video recording and augmented reality.

Java - Advanced One to one video call

This web application consists on an advanced one to one video call using WebRTC technology. It is an improved version of the one 2 one call tutorial).

注解

This tutorial has been configured to use https. Follow the instructions to secure your application.

For the impatient: running this example

First of all, you should install Kurento Media Server to run this demo. Please visit the installation guide for further information.

To launch the application, you need to clone the GitHub project where this demo is hosted, and then run the main class:

git clone https://github.com/Kurento/kurento-tutorial-java.git
cd kurento-tutorial-java/kurento-one2one-call-advanced
git checkout 6.6.2
mvn compile exec:java

The web application starts on port 8443 in the localhost by default. Therefore, open the URL https://localhost:8443/ in a WebRTC compliant browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the flag kms.url to the JVM executing the demo. As we’ll be using maven, you should execute the following command

mvn compile exec:java -Dkms.url=ws://kms_host:kms_port/kurento
Understanding this example

This application incorporates the recording capability provided by the Kurento Media Server in a one to one video communication. In addition, a filter element (FaceOverlayFilter) is placed between the WebRtcEndpoints of the Media Pipeline. The following picture shows an screenshot of this demo running in a web browser:

Advanced one to one video call screenshot

Advanced one to one video call screenshot

The interface of the application (an HTML web page) is composed by two HTML5 video tags: one for the local video camera stream (the caller stream, the smaller video in the picture) and other for the remote peer in the call (the callee stream, the bigger video in the picture). If two users, A and B, are using the application, the media flow goes this way: The video camera stream of user A is sent to the Kurento Media Server and sent again to the user B. On the other hand, user B sends its video camera stream to Kurento and then it is sent to user A.

This application is implemented by means of two Media Pipeline ‘s. First, the rich real-time WebRTC communication is performed two WebRtcEndpoints interconnected, and with a FaceOverlayFilter in between them. In addition and a RecorderEndpoint is used to store both streams in the file system of the Kurento Media Server. This media pipeline is illustrated in the following picture:

Advanced one to one video call media pipeline (1)

Advanced one to one video call media pipeline (1)

A second media pipeline is needed to play the previously recorded media. This pipeline is composed by a PlayerEndpoint which reads the files stored in the Kurento Media Server. This media element injects the media in a WebRtcEndpoint which is charge to transport the media to the HTML5 video tag in the browser:

Advanced one to one video call media pipeline (2)

Advanced one to one video call media pipeline (2)

注解

The playback of a static file can be done in several ways. In addition to this media pipeline (PlayerEndpoint -> WebRtcEndpoint) the recorded file could be served directly by an HTTP server.

To communicate the client with the server to manage calls we have designed a signaling protocol based on JSON messages over WebSocket ‘s. The normal sequence between client and server would be as follows:

  1. User A is registered in the server with his name
  2. User B is registered in the server with her name
  3. User A wants to call to User B
  4. User B accepts the incoming call
  5. The communication is established and media is flowing between User A and User B
  6. One of the users finishes the video communication
  7. One of the users play the recorded media

This is very simple protocol designed to show a simple one to one call application implemented with Kurento. In a professional application it can be improved, for example implementing seeking user, ordered finish, among other functions.

Assuming that User A is using Client A and User B is using Client B, we can draw the following sequence diagram with detailed messages between clients and server. The following diagram shows the two parts of the signaling protocol: first the enhanced real-time communication is performed, and then the playback of the recorded file is carried out.

Advanced one to one video call signaling protocol

Advanced one to one video call signaling protocol

As you can see in the diagram, SDP and ICE candidates need to be interchanged between client and server to establish the WebRTC connection between the Kurento client and server. Specifically, the SDP negotiation connects the WebRtcPeer in the browser with the WebRtcEndpoint in the server.

The following sections describe in detail the server-side, the client-side, and how to run the demo. The complete source code of this demo can be found in GitHub.

Application Server Logic

As in the Magic Mirror tutorial, this demo has been developed using Java and Spring Boot.

注解

You can use whatever Java server side technology you prefer to build web applications with Kurento. For example, a pure Java EE application, SIP Servlets, Play, Vertex, etc. We have choose Spring Boot for convenience.

In the following figure you can see a class diagram of the server side code:

Server-side class diagram of the advanced one to one video call app

Server-side class diagram of the advanced one to one video call app

The main class of this demo is named One2OneCallAdvApp. As you can see, the KurentoClient is instantiated in this class as a Spring Bean.

@EnableWebSocket
@SpringBootApplication
public class One2OneCallAdvApp implements WebSocketConfigurer {

   final static String DEFAULT_APP_SERVER_URL = "https://localhost:8443";

   @Bean
   public CallHandler callHandler() {
      return new CallHandler();
   }

   @Bean
   public UserRegistry registry() {
      return new UserRegistry();
   }

   @Bean
   public KurentoClient kurentoClient() {
      return KurentoClient.create();
   }

   public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
      registry.addHandler(callHandler(), "/call");
   }

   public static void main(String[] args) throws Exception {
      new SpringApplication(One2OneCallAdvApp.class).run(args);
   }

}

This web application follows a Single Page Application architecture (SPA), and uses a WebSocket to communicate client with server by means of requests and responses. Specifically, the main app class implements the interface WebSocketConfigurer to register a WebSocketHanlder to process WebSocket requests in the path /call.

CallHandler class implements TextWebSocketHandler to handle text WebSocket requests. The central piece of this class is the method handleTextMessage. This method implements the actions for requests, returning responses through the WebSocket. In other words, it implements the server part of the signaling protocol depicted in the previous sequence diagram.

In the designed protocol there are five different kind of incoming messages to the Server : register, call, incomingCallResponse, onIceCandidate and play. These messages are treated in the switch clause, taking the proper steps in each case.

public class CallHandler extends TextWebSocketHandler {

   private static final Logger log = LoggerFactory
         .getLogger(CallHandler.class);
   private static final Gson gson = new GsonBuilder().create();

   private final ConcurrentHashMap<String, MediaPipeline> pipelines = new ConcurrentHashMap<String, MediaPipeline>();

   @Autowired
   private KurentoClient kurento;

   @Autowired
   private UserRegistry registry;

   @Override
   public void handleTextMessage(WebSocketSession session, TextMessage message)
         throws Exception {
      JsonObject jsonMessage = gson.fromJson(message.getPayload(),
            JsonObject.class);
      UserSession user = registry.getBySession(session);

      if (user != null) {
         log.debug("Incoming message from user '{}': {}", user.getName(),
               jsonMessage);
      } else {
         log.debug("Incoming message from new user: {}", jsonMessage);
      }

      switch (jsonMessage.get("id").getAsString()) {
      case "register":
         register(session, jsonMessage);
         break;
      case "call":
         call(user, jsonMessage);
         break;
      case "incomingCallResponse":
         incomingCallResponse(user, jsonMessage);
         break;
      case "play":
         play(user, jsonMessage);
         break;
      case "onIceCandidate": {
         JsonObject candidate = jsonMessage.get("candidate")
               .getAsJsonObject();

         if (user != null) {
            IceCandidate cand = new IceCandidate(candidate.get("candidate")
                  .getAsString(), candidate.get("sdpMid").getAsString(),
                  candidate.get("sdpMLineIndex").getAsInt());
            user.addCandidate(cand);
         }
         break;
      }
      case "stop":
         stop(session);
         releasePipeline(user);
      case "stopPlay":
         releasePipeline(user);
      default:
         break;
      }
   }

   private void register(WebSocketSession session, JsonObject jsonMessage)
         throws IOException {
      ...
   }

   private void call(UserSession caller, JsonObject jsonMessage)
         throws IOException {
      ...
   }

   private void incomingCallResponse(final UserSession callee,
         JsonObject jsonMessage) throws IOException {
      ...
   }

   public void stop(WebSocketSession session) throws IOException {
      ...
   }

   public void releasePipeline(UserSession session) throws IOException {
      ...
   }

   private void play(final UserSession session, JsonObject jsonMessage)
         throws IOException {
      ...
   }

   @Override
   public void afterConnectionClosed(WebSocketSession session,
         CloseStatus status) throws Exception {
      stop(session);
      registry.removeBySession(session);
   }

}

In the following snippet, we can see the register method. Basically, it obtains the name attribute from register message and check if there are a registered user with that name. If not, the new user is registered and an acceptance message is sent to it.

private void register(WebSocketSession session, JsonObject jsonMessage)
      throws IOException {
   String name = jsonMessage.getAsJsonPrimitive("name").getAsString();

   UserSession caller = new UserSession(session, name);
   String responseMsg = "accepted";
   if (name.isEmpty()) {
      responseMsg = "rejected: empty user name";
   } else if (registry.exists(name)) {
      responseMsg = "rejected: user '" + name + "' already registered";
   } else {
      registry.register(caller);
   }

   JsonObject response = new JsonObject();
   response.addProperty("id", "resgisterResponse");
   response.addProperty("response", responseMsg);
   caller.sendMessage(response);
}

In the call method, the server checks if there are a registered user with the name specified in to message attribute and send an incomingCall message to it. Or, if there isn’t any user with that name, a callResponse message is sent to caller rejecting the call.

private void call(UserSession caller, JsonObject jsonMessage)
      throws IOException {
   String to = jsonMessage.get("to").getAsString();
   String from = jsonMessage.get("from").getAsString();
   JsonObject response = new JsonObject();

   if (registry.exists(to)) {
      UserSession callee = registry.getByName(to);
      caller.setSdpOffer(jsonMessage.getAsJsonPrimitive("sdpOffer")
            .getAsString());
      caller.setCallingTo(to);

      response.addProperty("id", "incomingCall");
      response.addProperty("from", from);

      callee.sendMessage(response);
      callee.setCallingFrom(from);
   } else {
      response.addProperty("id", "callResponse");
      response.addProperty("response", "rejected");
      response.addProperty("message", "user '" + to
            + "' is not registered");

      caller.sendMessage(response);
   }
}

In the incomingCallResponse method, if the callee user accepts the call, it is established and the media elements are created to connect the caller with the callee. Basically, the server creates a CallMediaPipeline object, to encapsulate the media pipeline creation and management. Then, this object is used to negotiate media interchange with user’s browsers.

As explained in the Magic Mirror tutorial, the negotiation between WebRTC peer in the browser and WebRtcEndpoint in Kurento Server is made by means of SDP generation at the client (offer) and SDP generation at the server (answer). The SDP answers are generated with the Kurento Java Client inside the class CallMediaPipeline (as we see in a moment). The methods used to generate SDP are generateSdpAnswerForCallee(calleeSdpOffer) and generateSdpAnswerForCaller(callerSdpOffer):

private void incomingCallResponse(final UserSession callee,
      JsonObject jsonMessage) throws IOException {
   String callResponse = jsonMessage.get("callResponse").getAsString();
   String from = jsonMessage.get("from").getAsString();
   final UserSession calleer = registry.getByName(from);
   String to = calleer.getCallingTo();

   if ("accept".equals(callResponse)) {
      log.debug("Accepted call from '{}' to '{}'", from, to);

      CallMediaPipeline callMediaPipeline = new CallMediaPipeline(
            kurento, from, to);
      pipelines.put(calleer.getSessionId(),
            callMediaPipeline.getPipeline());
      pipelines.put(callee.getSessionId(),
            callMediaPipeline.getPipeline());

      String calleeSdpOffer = jsonMessage.get("sdpOffer").getAsString();
      String calleeSdpAnswer = callMediaPipeline
            .generateSdpAnswerForCallee(calleeSdpOffer);

      callee.setWebRtcEndpoint(callMediaPipeline.getCalleeWebRtcEP());
      callMediaPipeline.getCalleeWebRtcEP().addIceCandidateFoundListener(
            new EventListener<IceCandidateFoundEvent>() {

               @Override
               public void onEvent(IceCandidateFoundEvent event) {
                  JsonObject response = new JsonObject();
                  response.addProperty("id", "iceCandidate");
                  response.add("candidate", JsonUtils
                        .toJsonObject(event.getCandidate()));
                  try {
                     synchronized (callee.getSession()) {
                        callee.getSession()
                              .sendMessage(
                                    new TextMessage(response
                                          .toString()));
                     }
                  } catch (IOException e) {
                     log.debug(e.getMessage());
                  }
               }
            });

      JsonObject startCommunication = new JsonObject();
      startCommunication.addProperty("id", "startCommunication");
      startCommunication.addProperty("sdpAnswer", calleeSdpAnswer);

      synchronized (callee) {
         callee.sendMessage(startCommunication);
      }

      callMediaPipeline.getCalleeWebRtcEP().gatherCandidates();

      String callerSdpOffer = registry.getByName(from).getSdpOffer();

      calleer.setWebRtcEndpoint(callMediaPipeline.getCallerWebRtcEP());
      callMediaPipeline.getCallerWebRtcEP().addIceCandidateFoundListener(
            new EventListener<IceCandidateFoundEvent>() {

               @Override
               public void onEvent(IceCandidateFoundEvent event) {
                  JsonObject response = new JsonObject();
                  response.addProperty("id", "iceCandidate");
                  response.add("candidate", JsonUtils
                        .toJsonObject(event.getCandidate()));
                  try {
                     synchronized (calleer.getSession()) {
                        calleer.getSession()
                              .sendMessage(
                                    new TextMessage(response
                                          .toString()));
                     }
                  } catch (IOException e) {
                     log.debug(e.getMessage());
                  }
               }
            });

      String callerSdpAnswer = callMediaPipeline
            .generateSdpAnswerForCaller(callerSdpOffer);

      JsonObject response = new JsonObject();
      response.addProperty("id", "callResponse");
      response.addProperty("response", "accepted");
      response.addProperty("sdpAnswer", callerSdpAnswer);

      synchronized (calleer) {
         calleer.sendMessage(response);
      }

      callMediaPipeline.getCallerWebRtcEP().gatherCandidates();

      callMediaPipeline.record();

   } else {
      JsonObject response = new JsonObject();
      response.addProperty("id", "callResponse");
      response.addProperty("response", "rejected");
      calleer.sendMessage(response);
   }
}

Finally, the play method instantiates a PlayMediaPipeline object, which is used to create Media Pipeline in charge of the playback of the recorded streams in the Kurento Media Server.

private void play(final UserSession session, JsonObject jsonMessage)
      throws IOException {
   String user = jsonMessage.get("user").getAsString();
   log.debug("Playing recorded call of user '{}'", user);

   JsonObject response = new JsonObject();
   response.addProperty("id", "playResponse");

   if (registry.getByName(user) != null
         && registry.getBySession(session.getSession()) != null) {
      final PlayMediaPipeline playMediaPipeline = new PlayMediaPipeline(
            kurento, user, session.getSession());
      String sdpOffer = jsonMessage.get("sdpOffer").getAsString();

      session.setPlayingWebRtcEndpoint(playMediaPipeline.getWebRtc());

      playMediaPipeline.getPlayer().addEndOfStreamListener(
            new EventListener<EndOfStreamEvent>() {
               @Override
               public void onEvent(EndOfStreamEvent event) {
                  UserSession user = registry
                        .getBySession(session.getSession());
                  releasePipeline(user);
                  playMediaPipeline.sendPlayEnd(session.getSession());
               }
            });

      playMediaPipeline.getWebRtc().addIceCandidateFoundListener(
            new EventListener<IceCandidateFoundEvent>() {

               @Override
               public void onEvent(IceCandidateFoundEvent event) {
                  JsonObject response = new JsonObject();
                  response.addProperty("id", "iceCandidate");
                  response.add("candidate", JsonUtils
                        .toJsonObject(event.getCandidate()));
                  try {
                     synchronized (session) {
                        session.getSession()
                              .sendMessage(
                                    new TextMessage(response
                                          .toString()));
                     }
                  } catch (IOException e) {
                     log.debug(e.getMessage());
                  }
               }
            });

      String sdpAnswer = playMediaPipeline.generateSdpAnswer(sdpOffer);

      response.addProperty("response", "accepted");

      response.addProperty("sdpAnswer", sdpAnswer);

      playMediaPipeline.play();
      pipelines.put(session.getSessionId(),
            playMediaPipeline.getPipeline());
      synchronized (session.getSession()) {
         session.sendMessage(response);
      }

      playMediaPipeline.getWebRtc().gatherCandidates();

   } else {
      response.addProperty("response", "rejected");
      response.addProperty("error", "No recording for user '" + user
            + "'. Please type a correct user in the 'Peer' field.");
      session.getSession().sendMessage(
            new TextMessage(response.toString()));
   }
}

The media logic in this demo is implemented in the classes CallMediaPipeline and PlayMediaPipeline. The first media pipeline consists on two WebRtcEndpoint elements interconnected with a FaceOverlayFilter in between, and also with and RecorderEndpoint to carry out the recording of the WebRTC communication. Please take note that the WebRtc endpoints needs to be connected twice, one for each media direction. In this class we can see the implementation of methods generateSdpAnswerForCaller and generateSdpAnswerForCallee. These methods delegate to WebRtc endpoints to create the appropriate answer.

public class CallMediaPipeline {

   private static final SimpleDateFormat df = new SimpleDateFormat(
         "yyyy-MM-dd_HH-mm-ss-S");
   public static final String RECORDING_PATH = "file:///tmp/"
         + df.format(new Date()) + "-";
   public static final String RECORDING_EXT = ".webm";

   private final MediaPipeline pipeline;
   private final WebRtcEndpoint webRtcCaller;
   private final WebRtcEndpoint webRtcCallee;
   private final RecorderEndpoint recorderCaller;
   private final RecorderEndpoint recorderCallee;

   public CallMediaPipeline(KurentoClient kurento, String from, String to) {

      // Media pipeline
      pipeline = kurento.createMediaPipeline();

      // Media Elements (WebRtcEndpoint, RecorderEndpoint, FaceOverlayFilter)
      webRtcCaller = new WebRtcEndpoint.Builder(pipeline).build();
      webRtcCallee = new WebRtcEndpoint.Builder(pipeline).build();

      recorderCaller = new RecorderEndpoint.Builder(pipeline, RECORDING_PATH
            + from + RECORDING_EXT).build();
      recorderCallee = new RecorderEndpoint.Builder(pipeline, RECORDING_PATH
            + to + RECORDING_EXT).build();

      String appServerUrl = System.getProperty("app.server.url",
            One2OneCallAdvApp.DEFAULT_APP_SERVER_URL);
      FaceOverlayFilter faceOverlayFilterCaller = new FaceOverlayFilter.Builder(
            pipeline).build();
      faceOverlayFilterCaller.setOverlayedImage(appServerUrl
            + "/img/mario-wings.png", -0.35F, -1.2F, 1.6F, 1.6F);

      FaceOverlayFilter faceOverlayFilterCallee = new FaceOverlayFilter.Builder(
            pipeline).build();
      faceOverlayFilterCallee.setOverlayedImage(
            appServerUrl + "/img/Hat.png", -0.2F, -1.35F, 1.5F, 1.5F);

      // Connections
      webRtcCaller.connect(faceOverlayFilterCaller);
      faceOverlayFilterCaller.connect(webRtcCallee);
      faceOverlayFilterCaller.connect(recorderCaller);

      webRtcCallee.connect(faceOverlayFilterCallee);
      faceOverlayFilterCallee.connect(webRtcCaller);
      faceOverlayFilterCallee.connect(recorderCallee);
   }

   public void record() {
      recorderCaller.record();
      recorderCallee.record();
   }

   public String generateSdpAnswerForCaller(String sdpOffer) {
      return webRtcCaller.processOffer(sdpOffer);
   }

   public String generateSdpAnswerForCallee(String sdpOffer) {
      return webRtcCallee.processOffer(sdpOffer);
   }

   public MediaPipeline getPipeline() {
      return pipeline;
   }

   public WebRtcEndpoint getCallerWebRtcEP() {
      return webRtcCaller;
   }

   public WebRtcEndpoint getCalleeWebRtcEP() {
      return webRtcCallee;
   }
}

注解

Notice the hat URLs are provided by the application server and consumed by the KMS. This logic is assuming that the application server is hosted in local (localhost), and by the default the hat URLs are https://localhost:8443/img/mario-wings.png and https://localhost:8443/img/Hat.png. If your application server is hosted in a different host, it can be easily changed by means of the configuration parameter app.server.url, for example:

mvn compile exec:java -Dapp.server.url=https://app_server_host:app_server_port

The second media pipeline consists on a PlayerEndpoint connected to a WebRtcEndpoint. The PlayerEndpoint reads the previously recorded media in the file system of the Kurento Media Server. The WebRtcEndpoint is used in receive-only mode.

public class PlayMediaPipeline {

   private static final Logger log = LoggerFactory
         .getLogger(PlayMediaPipeline.class);

   private WebRtcEndpoint webRtc;
   private PlayerEndpoint player;

   public PlayMediaPipeline(KurentoClient kurento, String user,
         final WebSocketSession session) {
      // Media pipeline
      MediaPipeline pipeline = kurento.createMediaPipeline();

      // Media Elements (WebRtcEndpoint, PlayerEndpoint)
      webRtc = new WebRtcEndpoint.Builder(pipeline).build();
      player = new PlayerEndpoint.Builder(pipeline, RECORDING_PATH + user
            + RECORDING_EXT).build();

      // Connection
      player.connect(webRtc);

      // Player listeners
      player.addErrorListener(new EventListener<ErrorEvent>() {
         @Override
         public void onEvent(ErrorEvent event) {
            log.info("ErrorEvent: {}", event.getDescription());
            sendPlayEnd(session);
         }
      });
   }

   public void sendPlayEnd(WebSocketSession session) {
      try {
         JsonObject response = new JsonObject();
         response.addProperty("id", "playEnd");
         session.sendMessage(new TextMessage(response.toString()));
      } catch (IOException e) {
         log.error("Error sending playEndOfStream message", e);
      }
   }

   public void play() {
      player.play();
   }

   public String generateSdpAnswer(String sdpOffer) {
      return webRtc.processOffer(sdpOffer);
   }

   public MediaPipeline getPipeline() {
      return pipeline;
   }

   public WebRtcEndpoint getWebRtc() {
      return webRtc;
   }

   public PlayerEndpoint getPlayer() {
      return player;
   }

}
Client-Side

Let’s move now to the client-side of the application. To call the previously created WebSocket service in the server-side, we use the JavaScript class WebSocket. We use a specific Kurento JavaScript library called kurento-utils.js to simplify the WebRTC interaction with the server. This library depends on adapter.js, which is a JavaScript WebRTC utility maintained by Google that abstracts away browser differences. Finally jquery.js is also needed in this application.

These libraries are linked in the index.html web page, and are used in the index.js.

In the following snippet we can see the creation of the WebSocket (variable ws) in the path /call. Then, the onmessage listener of the WebSocket is used to implement the JSON signaling protocol in the client-side. Notice that there are six incoming messages to client: resgisterResponse, callResponse, incomingCall, startCommunication, iceCandidate and play. Convenient actions are taken to implement each step in the communication. On the one hand, in functions call and incomingCall (for caller and callee respectively), the function WebRtcPeer.WebRtcPeerSendrecv of kurento-utils.js is used to start a WebRTC communication. On the other hand in the function play, the function WebRtcPeer.WebRtcPeerRecvonly is called since the WebRtcEndpoint is used in receive-only.

var ws = new WebSocket('ws://' + location.host + '/call');

ws.onmessage = function(message) {
   var parsedMessage = JSON.parse(message.data);
   console.info('Received message: ' + message.data);

   switch (parsedMessage.id) {
   case 'resgisterResponse':
      resgisterResponse(parsedMessage);
      break;
   case 'callResponse':
      callResponse(parsedMessage);
      break;
   case 'incomingCall':
      incomingCall(parsedMessage);
      break;
   case 'startCommunication':
      startCommunication(parsedMessage);
      break;
   case 'stopCommunication':
      console.info("Communication ended by remote peer");
      stop(true);
      break;
   case 'playResponse':
      playResponse(parsedMessage);
      break;
   case 'playEnd':
      playEnd();
      break;
   case 'iceCandidate':
       webRtcPeer.addIceCandidate(parsedMessage.candidate, function (error) {
        if (!error) return;
         console.error("Error adding candidate: " + error);
       });
       break;
   default:
      console.error('Unrecognized message', parsedMessage);
   }
}

function incomingCall(message) {
   // If bussy just reject without disturbing user
   if (callState != NO_CALL && callState != POST_CALL) {
      var response = {
         id : 'incomingCallResponse',
         from : message.from,
         callResponse : 'reject',
         message : 'bussy'
      };
      return sendMessage(response);
   }

   setCallState(DISABLED);
   if (confirm('User ' + message.from
         + ' is calling you. Do you accept the call?')) {
      showSpinner(videoInput, videoOutput);

      from = message.from;
      var options = {
               localVideo: videoInput,
               remoteVideo: videoOutput,
               onicecandidate: onIceCandidate
             }
       webRtcPeer = new kurentoUtils.WebRtcPeer.WebRtcPeerSendrecv(options,
         function (error) {
           if(error) {
              return console.error(error);
           }
           this.generateOffer (onOfferIncomingCall);
         });
   } else {
      var response = {
         id : 'incomingCallResponse',
         from : message.from,
         callResponse : 'reject',
         message : 'user declined'
      };
      sendMessage(response);
      stop();
   }
}

function call() {
   if (document.getElementById('peer').value == '') {
      document.getElementById('peer').focus();
      window.alert("You must specify the peer name");
      return;
   }
   setCallState(DISABLED);
   showSpinner(videoInput, videoOutput);

   var options = {
            localVideo: videoInput,
            remoteVideo: videoOutput,
            onicecandidate: onIceCandidate
          }
   webRtcPeer = new kurentoUtils.WebRtcPeer.WebRtcPeerSendrecv(options,
      function (error) {
        if(error) {
           return console.error(error);
        }
        this.generateOffer (onOfferCall);
   });
}

function play() {
   var peer = document.getElementById('peer').value;
   if (peer == '') {
      window.alert("You must insert the name of the user recording to be played (field 'Peer')");
      document.getElementById('peer').focus();
      return;
   }

   document.getElementById('videoSmall').style.display = 'none';
   setCallState(DISABLED);
   showSpinner(videoOutput);

   var options = {
            remoteVideo: videoOutput,
            onicecandidate: onIceCandidate
          }
   webRtcPeer = new kurentoUtils.WebRtcPeer.WebRtcPeerRecvonly(options,
      function (error) {
        if(error) {
           return console.error(error);
        }
        this.generateOffer (onOfferPlay);
   });
}

function stop(message) {
   var stopMessageId = (callState == IN_CALL) ? 'stop' : 'stopPlay';
   setCallState(POST_CALL);
   if (webRtcPeer) {
      webRtcPeer.dispose();
      webRtcPeer = null;

      if (!message) {
         var message = {
            id : stopMessageId
         }
         sendMessage(message);
      }
   }
   hideSpinner(videoInput, videoOutput);
   document.getElementById('videoSmall').style.display = 'block';
}
Dependencies

This Java Spring application is implemented using Maven. The relevant part of the pom.xml is where Kurento dependencies are declared. As the following snippet shows, we need two dependencies: the Kurento Client Java dependency (kurento-client) and the JavaScript Kurento utility library (kurento-utils) for the client-side. Other client libraries are managed with webjars:

<dependencies>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-client</artifactId>
   </dependency>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-utils-js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars</groupId>
      <artifactId>webjars-locator</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>bootstrap</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>demo-console</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>draggabilly</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>adapter.js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>jquery</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>ekko-lightbox</artifactId>
   </dependency>
</dependencies>

注解

We are in active development. You can find the latest version of Kurento Java Client at Maven Central.

Kurento Java Client has a minimum requirement of Java 7. Hence, you need to include the following properties in your pom:

<maven.compiler.target>1.7</maven.compiler.target>
<maven.compiler.source>1.7</maven.compiler.source>

WebRTC many-to-many video call (Group call)

This tutorial connects several participants to the same video conference. A group call will ocnsist, in the media server side, in N*N WebRTC endpoints, where N is the number of clients connected to that conference.

Java - Group Call

This tutorial shows how to work wih the concept of rooms, allowing to connect several clients between them using WebRTC technology, creating a multiconference.

注解

This tutorial has been configured to use https. Follow the instructions to secure your application.

For the impatient: running this example

You need to have installed the Kurento Media Server before running this example. Read the installation guide for further information.

To launch the application, you need to clone the GitHub project where this demo is hosted, and then run the main class:

git clone https://github.com/Kurento/kurento-tutorial-java.git
cd kurento-tutorial-java/kurento-group-call
git checkout 6.6.2
mvn compile exec:java

Access the application connecting to the URL https://localhost:8443/ in a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the flag kms.url to the JVM executing the demo. As we’ll be using maven, you should execute the following command

mvn compile exec:java -Dkms.url=ws://kms_host:kms_port/kurento
Understanding this example

This tutorial shows how to work with the concept of rooms. Each room will create its own pipeline, being isolated from the other rooms. Clients connecting to a certain room, will only be able to exchange media with clients in the same room.

Each client will send its own media, and in turn will receive the media from all the other participants. This means that there will be a total of n*n webrtc endpoints in each room, where n is the number of clients.

When a new client enters the room, a new webrtc will be created and negotiated receive the media on the server. On the other hand, all participant will be informed that a new user has connected. Then, all participants will request the server to receive the new participant’s media.

The newcomer, in turn, gets a list of all connected participants, and requests the server to receive the media from all the present clients in the room.

When a client leaves the room, all clients are informed by the server. Then, the client-side code requests the server to cancel all media elements related to the client that left.

This is a web application, and therefore it follows a client-server architecture. At the client-side, the logic is implemented in JavaScript. At the server-side, we use a Spring-Boot based server application consuming the Kurento Java Client API, to control Kurento Media Server capabilities. All in all, the high level architecture of this demo is three-tier. To communicate these entities, two WebSockets are used. First, a WebSocket is created between client and application server to implement a custom signaling protocol. Second, another WebSocket is used to perform the communication between the Kurento Java Client and the Kurento Media Server. This communication takes place using the Kurento Protocol. For further information on it, please see this page of the documentation.

The following sections analyze in depth the server (Java) and client-side (JavaScript) code of this application. The complete source code can be found in GitHub.

Application Server Logic

This demo has been developed using Java in the server-side with Spring Boot framework. This technology can be used to embed the Tomcat web server in the application and thus simplify the development process.

注解

You can use whatever Java server side technology you prefer to build web applications with Kurento. For example, a pure Java EE application, SIP Servlets, Play, Vert.x, etc. Here we chose Spring Boot for convenience.

The main class of this demo is GroupCalldApp. As you can see, the KurentoClient is instantiated in this class as a Spring Bean. This bean is used to create Kurento Media Pipelines, which are used to add media capabilities to the application. In this instantiation we see that we need to specify to the client library the location of the Kurento Media Server. In this example, we assume it is located at localhost listening in port 8888. If you reproduce this example you’ll need to insert the specific location of your Kurento Media Server instance there.

Once the Kurento Client has been instantiated, you are ready for communicating with Kurento Media Server and controlling its multimedia capabilities.

@EnableWebSocket
@SpringBootApplication
public class GroupCallApp implements WebSocketConfigurer {

  @Bean
  public UserRegistry registry() {
    return new UserRegistry();
  }

  @Bean
  public RoomManager roomManager() {
    return new RoomManager();
  }

  @Bean
  public CallHandler groupCallHandler() {
    return new CallHandler();
  }

  @Bean
  public KurentoClient kurentoClient() {
    return KurentoClient.create();
  }

  public static void main(String[] args) throws Exception {
    SpringApplication.run(GroupCallApp.class, args);
  }

  @Override
  public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
    registry.addHandler(groupCallHandler(), "/groupcall");
  }
}

This web application follows a Single Page Application architecture (SPA), and uses a WebSocket to communicate client with application server by means of requests and responses. Specifically, the main app class implements the interface WebSocketConfigurer to register a WebSocketHanlder to process WebSocket requests in the path /groupcall.

CallHandler class implements TextWebSocketHandler to handle text WebSocket requests. The central piece of this class is the method handleTextMessage. This method implements the actions for requests, returning responses through the WebSocket. In other words, it implements the server part of the signaling protocol depicted in the previous sequence diagram.

In the designed protocol there are five different kind of incoming messages to the application server: joinRoom, receiveVideoFrom, leaveRoom and onIceCandidate. These messages are treated in the switch clause, taking the proper steps in each case.

public class CallHandler extends TextWebSocketHandler {

  private static final Logger log = LoggerFactory.getLogger(CallHandler.class);

  private static final Gson gson = new GsonBuilder().create();

  @Autowired
  private RoomManager roomManager;

  @Autowired
  private UserRegistry registry;

  @Override
  public void handleTextMessage(WebSocketSession session, TextMessage message) throws Exception {
    final JsonObject jsonMessage = gson.fromJson(message.getPayload(), JsonObject.class);

    final UserSession user = registry.getBySession(session);

    if (user != null) {
      log.debug("Incoming message from user '{}': {}", user.getName(), jsonMessage);
    } else {
      log.debug("Incoming message from new user: {}", jsonMessage);
    }

    switch (jsonMessage.get("id").getAsString()) {
      case "joinRoom":
        joinRoom(jsonMessage, session);
        break;
      case "receiveVideoFrom":
        final String senderName = jsonMessage.get("sender").getAsString();
        final UserSession sender = registry.getByName(senderName);
        final String sdpOffer = jsonMessage.get("sdpOffer").getAsString();
        user.receiveVideoFrom(sender, sdpOffer);
        break;
      case "leaveRoom":
        leaveRoom(user);
        break;
      case "onIceCandidate":
        JsonObject candidate = jsonMessage.get("candidate").getAsJsonObject();

        if (user != null) {
          IceCandidate cand = new IceCandidate(candidate.get("candidate").getAsString(),
              candidate.get("sdpMid").getAsString(), candidate.get("sdpMLineIndex").getAsInt());
          user.addCandidate(cand, jsonMessage.get("name").getAsString());
        }
        break;
      default:
        break;
    }
  }

  @Override
  public void afterConnectionClosed(WebSocketSession session, CloseStatus status) throws Exception {
      ...
  }

  private void joinRoom(JsonObject params, WebSocketSession session) throws IOException {
      ...
  }

  private void leaveRoom(UserSession user) throws IOException {
      ...
  }
}

In the following snippet, we can see the afterConnectionClosed method. Basically, it removes the userSession from registry and throws out the user from the room.

@Override
public void afterConnectionClosed(WebSocketSession session, CloseStatus status) throws Exception {
   UserSession user = registry.removeBySession(session);
   roomManager.getRoom(user.getRoomName()).leave(user);
}

In the joinRoom method, the server checks if there are a registered room with the name specified, add the user into this room and registries the user.

private void joinRoom(JsonObject params, WebSocketSession session) throws IOException {
   final String roomName = params.get("room").getAsString();
   final String name = params.get("name").getAsString();
   log.info("PARTICIPANT {}: trying to join room {}", name, roomName);

   Room room = roomManager.getRoom(roomName);
   final UserSession user = room.join(name, session);
   registry.register(user);
}

The leaveRoom method finish the video call from one user.

private void leaveRoom(UserSession user) throws IOException {
    final Room room = roomManager.getRoom(user.getRoomName());
    room.leave(user);
    if (room.getParticipants().isEmpty()) {
      roomManager.removeRoom(room);
    }
}
Client-Side Logic

Let’s move now to the client-side of the application. To call the previously created WebSocket service in the server-side, we use the JavaScript class WebSocket. We use a specific Kurento JavaScript library called kurento-utils.js to simplify the WebRTC interaction with the server. This library depends on adapter.js, which is a JavaScript WebRTC utility maintained by Google that abstracts away browser differences. Finally jquery.js is also needed in this application.

These libraries are linked in the index.html web page, and are used in the conferenceroom.js. In the following snippet we can see the creation of the WebSocket (variable ws) in the path /groupcall. Then, the onmessage listener of the WebSocket is used to implement the JSON signaling protocol in the client-side. Notice that there are three incoming messages to client: existingParticipants, newParticipantArrived, participantLeft, receiveVideoAnswer and iceCandidate. Convenient actions are taken to implement each step in the communication. For example, in functions start the function WebRtcPeer.WebRtcPeerSendrecv of kurento-utils.js is used to start a WebRTC communication.

var ws = new WebSocket('wss://' + location.host + '/groupcall');
var participants = {};
var name;

window.onbeforeunload = function() {
   ws.close();
};

ws.onmessage = function(message) {
   var parsedMessage = JSON.parse(message.data);
   console.info('Received message: ' + message.data);

   switch (parsedMessage.id) {
   case 'existingParticipants':
      onExistingParticipants(parsedMessage);
      break;
   case 'newParticipantArrived':
      onNewParticipant(parsedMessage);
      break;
   case 'participantLeft':
      onParticipantLeft(parsedMessage);
      break;
   case 'receiveVideoAnswer':
      receiveVideoResponse(parsedMessage);
      break;
   case 'iceCandidate':
      participants[parsedMessage.name].rtcPeer.addIceCandidate(parsedMessage.candidate, function (error) {
           if (error) {
            console.error("Error adding candidate: " + error);
            return;
           }
       });
       break;
   default:
      console.error('Unrecognized message', parsedMessage);
   }
}

function register() {
   name = document.getElementById('name').value;
   var room = document.getElementById('roomName').value;

   document.getElementById('room-header').innerText = 'ROOM ' + room;
   document.getElementById('join').style.display = 'none';
   document.getElementById('room').style.display = 'block';

   var message = {
      id : 'joinRoom',
      name : name,
      room : room,
   }
   sendMessage(message);
}

function onNewParticipant(request) {
   receiveVideo(request.name);
}

function receiveVideoResponse(result) {
   participants[result.name].rtcPeer.processAnswer (result.sdpAnswer, function (error) {
      if (error) return console.error (error);
   });
}

function callResponse(message) {
   if (message.response != 'accepted') {
      console.info('Call not accepted by peer. Closing call');
      stop();
   } else {
      webRtcPeer.processAnswer(message.sdpAnswer, function (error) {
         if (error) return console.error (error);
      });
   }
}

function onExistingParticipants(msg) {
   var constraints = {
      audio : true,
      video : {
         mandatory : {
            maxWidth : 320,
            maxFrameRate : 15,
            minFrameRate : 15
         }
      }
   };
   console.log(name + " registered in room " + room);
   var participant = new Participant(name);
   participants[name] = participant;
   var video = participant.getVideoElement();

   var options = {
         localVideo: video,
         mediaConstraints: constraints,
         onicecandidate: participant.onIceCandidate.bind(participant)
       }
   participant.rtcPeer = new kurentoUtils.WebRtcPeer.WebRtcPeerSendonly(options,
      function (error) {
        if(error) {
           return console.error(error);
        }
        this.generateOffer (participant.offerToReceiveVideo.bind(participant));
   });

   msg.data.forEach(receiveVideo);
}

function leaveRoom() {
   sendMessage({
      id : 'leaveRoom'
   });

   for ( var key in participants) {
      participants[key].dispose();
   }

   document.getElementById('join').style.display = 'block';
   document.getElementById('room').style.display = 'none';

   ws.close();
}

function receiveVideo(sender) {
   var participant = new Participant(sender);
   participants[sender] = participant;
   var video = participant.getVideoElement();

   var options = {
      remoteVideo: video,
      onicecandidate: participant.onIceCandidate.bind(participant)
    }

   participant.rtcPeer = new kurentoUtils.WebRtcPeer.WebRtcPeerRecvonly(options,
         function (error) {
           if(error) {
              return console.error(error);
           }
           this.generateOffer (participant.offerToReceiveVideo.bind(participant));
   });;
}

function onParticipantLeft(request) {
   console.log('Participant ' + request.name + ' left');
   var participant = participants[request.name];
   participant.dispose();
   delete participants[request.name];
}

function sendMessage(message) {
   var jsonMessage = JSON.stringify(message);
   console.log('Senging message: ' + jsonMessage);
   ws.send(jsonMessage);
}
Dependencies

This Java Spring application is implemented using Maven. The relevant part of the pom.xml is where Kurento dependencies are declared. As the following snippet shows, we need two dependencies: the Kurento Client Java dependency (kurento-client) and the JavaScript Kurento utility library (kurento-utils) for the client-side. Other client libraries are managed with webjars:

<dependencies>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-client</artifactId>
   </dependency>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-utils-js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars</groupId>
      <artifactId>webjars-locator</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>bootstrap</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>demo-console</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>adapter.js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>jquery</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>ekko-lightbox</artifactId>
   </dependency>
</dependencies>

注解

We are in active development. You can find the latest version of Kurento Java Client at Maven Central.

Kurento Java Client has a minimum requirement of Java 7. Hence, you need to include the following properties in your pom:

<maven.compiler.target>1.7</maven.compiler.target>
<maven.compiler.source>1.7</maven.compiler.source>

Media Elements metadata

This tutorial detects and draws faces present in the webcam video. It connects filters: KmsDetectFaces and the KmsShowFaces.

Java - Metadata

This tutorial detects and draws faces into the webcam video. The demo connects two filters, the KmsDetectFaces and the KmsShowFaces.

注解

This tutorial has been configured to use https. Follow the instructions to secure your application.

For the impatient: running this example

You need to have installed the Kurento Media Server before running this example. Read the installation guide for further information.

To launch the application, you need to clone the GitHub project where this demo is hosted, and then run the main class:

git clone https://github.com/Kurento/kurento-tutorial-java.git
cd kurento-tutorial-java/kurento-metadata-example
git checkout 6.6.2
mvn compile exec:java

Access the application connecting to the URL https://localhost:8443/ in a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the flag kms.url to the JVM executing the demo. As we’ll be using maven, you should execute the following command

mvn compile exec:java -Dkms.url=ws://kms_host:kms_port/kurento

注解

This demo needs the kms-datachannelexample module installed in the media server. That module is available in the Kurento repositories, so it is possible to install it with:

sudo apt-get install kms-datachannelexample
Understanding this example

To implement this behavior we have to create a Media Pipeline composed by one WebRtcEndpoint and two filters KmsDetectFaces and KmsShowFaces. The first one detects faces into the image and it puts the info about the face (position and dimensions) into the buffer metadata. The second one reads the buffer metadata to find info about detected faces. If there is info about faces, the filter draws the faces into the image.

This is a web application, and therefore it follows a client-server architecture. At the client-side, the logic is implemented in JavaScript. At the server-side, we use a Spring-Boot based server application consuming the Kurento Java Client API, to control Kurento Media Server capabilities. All in all, the high level architecture of this demo is three-tier. To communicate these entities, two WebSockets are used. First, a WebSocket is created between client and application server to implement a custom signaling protocol. Second, another WebSocket is used to perform the communication between the Kurento Java Client and the Kurento Media Server. This communication takes place using the Kurento Protocol. For further information on it, please see this page of the documentation.

The following sections analyze in depth the server (Java) and client-side (JavaScript) code of this application. The complete source code can be found in GitHub.

Application Server Logic

This demo has been developed using Java in the server-side, based on the Spring Boot framework, which embeds a Tomcat web server within the generated maven artifact, and thus simplifies the development and deployment process.

注解

You can use whatever Java server side technology you prefer to build web applications with Kurento. For example, a pure Java EE application, SIP Servlets, Play, Vert.x, etc. Here we chose Spring Boot for convenience.

The main class of this demo is MetadataApp. As you can see, the KurentoClient is instantiated in this class as a Spring Bean. This bean is used to create Kurento Media Pipelines, which are used to add media capabilities to the application. In this instantiation we see that we need to specify to the client library the location of the Kurento Media Server. In this example, we assume it is located at localhost, listening in port 8888. If you reproduce this example, you’ll need to insert the specific location of your Kurento Media Server instance there.

Once the Kurento Client has been instantiated, you are ready for communicating with Kurento Media Server and controlling its multimedia capabilities.

@EnableWebSocket
@SpringBootApplication
public class MetadataApp implements WebSocketConfigurer {

  static final String DEFAULT_APP_SERVER_URL = "https://localhost:8443";

  @Bean
  public MetadataHandler handler() {
    return new MetadataHandler();
  }

  @Bean
  public KurentoClient kurentoClient() {
    return KurentoClient.create();
  }

  @Override
  public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
    registry.addHandler(handler(), "/metadata");
  }

  public static void main(String[] args) throws Exception {
    new SpringApplication(MetadataApp.class).run(args);
  }
}

This web application follows a Single Page Application architecture (SPA), and uses a WebSocket to communicate client with application server by means of requests and responses. Specifically, the main app class implements the interface WebSocketConfigurer to register a WebSocketHanlder to process WebSocket requests in the path /metadata.

MetadataHandler class implements TextWebSocketHandler to handle text WebSocket requests. The central piece of this class is the method handleTextMessage. This method implements the actions for requests, returning responses through the WebSocket. In other words, it implements the server part of the signaling protocol depicted in the previous sequence diagram.

In the designed protocol there are three different kinds of incoming messages to the Server : start, stop and onIceCandidates. These messages are treated in the switch clause, taking the proper steps in each case.

public class MetadataHandler extends TextWebSocketHandler {

  private final Logger log = LoggerFactory.getLogger(MetadataHandler.class);
  private static final Gson gson = new GsonBuilder().create();

  private final ConcurrentHashMap<String, UserSession> users = new ConcurrentHashMap<>();

  @Autowired
  private KurentoClient kurento;

  @Override
  public void handleTextMessage(WebSocketSession session, TextMessage message) throws Exception {
    JsonObject jsonMessage = gson.fromJson(message.getPayload(), JsonObject.class);

    log.debug("Incoming message: {}", jsonMessage);

    switch (jsonMessage.get("id").getAsString()) {
      case "start":
        start(session, jsonMessage);
        break;
      case "stop": {
        UserSession user = users.remove(session.getId());
        if (user != null) {
          user.release();
        }
        break;
      }
      case "onIceCandidate": {
        JsonObject jsonCandidate = jsonMessage.get("candidate").getAsJsonObject();

        UserSession user = users.get(session.getId());
        if (user != null) {
          IceCandidate candidate = new IceCandidate(jsonCandidate.get("candidate").getAsString(),
              jsonCandidate.get("sdpMid").getAsString(),
              jsonCandidate.get("sdpMLineIndex").getAsInt());
          user.addCandidate(candidate);
        }
        break;
      }
      default:
        sendError(session, "Invalid message with id " + jsonMessage.get("id").getAsString());
        break;
    }
  }

  private void start(final WebSocketSession session, JsonObject jsonMessage) {
    ...
  }

  private void sendError(WebSocketSession session, String message) {
   ...
  }
}

In the following snippet, we can see the start method. It handles the ICE candidates gathering, creates a Media Pipeline, creates the Media Elements (WebRtcEndpoint, KmsShowFaces and KmsDetectFaces) and make the connections among them. A startResponse message is sent back to the client with the SDP answer.

private void start(final WebSocketSession session, JsonObject jsonMessage) {
   try {
      // User session
      UserSession user = new UserSession();
      MediaPipeline pipeline = kurento.createMediaPipeline();
      user.setMediaPipeline(pipeline);
      WebRtcEndpoint webRtcEndpoint = new WebRtcEndpoint.Builder(pipeline).build();
      user.setWebRtcEndpoint(webRtcEndpoint);
      users.put(session.getId(), user);

      // ICE candidates
      webRtcEndpoint.addIceCandidateFoundListener(new EventListener<IceCandidateFoundEvent>() {
        @Override
        public void onEvent(IceCandidateFoundEvent event) {
          JsonObject response = new JsonObject();
          response.addProperty("id", "iceCandidate");
          response.add("candidate", JsonUtils.toJsonObject(event.getCandidate()));
          try {
            synchronized (session) {
              session.sendMessage(new TextMessage(response.toString()));
            }
          } catch (IOException e) {
            log.debug(e.getMessage());
          }
        }
      });

      // Media logic
      KmsShowFaces showFaces = new KmsShowFaces.Builder(pipeline).build();
      KmsDetectFaces detectFaces = new KmsDetectFaces.Builder(pipeline).build();

      webRtcEndpoint.connect(detectFaces);
      detectFaces.connect(showFaces);
      showFaces.connect(webRtcEndpoint);

      // SDP negotiation (offer and answer)
      String sdpOffer = jsonMessage.get("sdpOffer").getAsString();
      String sdpAnswer = webRtcEndpoint.processOffer(sdpOffer);

      JsonObject response = new JsonObject();
      response.addProperty("id", "startResponse");
      response.addProperty("sdpAnswer", sdpAnswer);

      synchronized (session) {
        session.sendMessage(new TextMessage(response.toString()));
      }

      webRtcEndpoint.gatherCandidates();

    } catch (Throwable t) {
      sendError(session, t.getMessage());
    }
}

The sendError method is quite simple: it sends an error message to the client when an exception is caught in the server-side.

private void sendError(WebSocketSession session, String message) {
   try {
      JsonObject response = new JsonObject();
      response.addProperty("id", "error");
      response.addProperty("message", message);
      session.sendMessage(new TextMessage(response.toString()));
   } catch (IOException e) {
      log.error("Exception sending message", e);
   }
}
Client-Side Logic

Let’s move now to the client-side of the application. To call the previously created WebSocket service in the server-side, we use the JavaScript class WebSocket. We use a specific Kurento JavaScript library called kurento-utils.js to simplify the WebRTC interaction with the server. This library depends on adapter.js, which is a JavaScript WebRTC utility maintained by Google that abstracts away browser differences. Finally jquery.js is also needed in this application.

These libraries are linked in the index.html web page, and are used in the index.js. In the following snippet we can see the creation of the WebSocket (variable ws) in the path /metadata. Then, the onmessage listener of the WebSocket is used to implement the JSON signaling protocol in the client-side. Notice that there are three incoming messages to client: startResponse, error, and iceCandidate. Convenient actions are taken to implement each step in the communication. For example, in functions start the function WebRtcPeer.WebRtcPeerSendrecv of kurento-utils.js is used to start a WebRTC communication.

 var ws = new WebSocket('wss://' + location.host + '/metadata');

 ws.onmessage = function(message) {
   var parsedMessage = JSON.parse(message.data);
   console.info('Received message: ' + message.data);

   switch (parsedMessage.id) {
   case 'startResponse':
      startResponse(parsedMessage);
      break;
   case 'error':
      if (state == I_AM_STARTING) {
         setState(I_CAN_START);
      }
      onError("Error message from server: " + parsedMessage.message);
      break;
   case 'iceCandidate':
      webRtcPeer.addIceCandidate(parsedMessage.candidate, function(error) {
         if (error) {
            console.error("Error adding candidate: " + error);
            return;
         }
      });
      break;
   default:
      if (state == I_AM_STARTING) {
         setState(I_CAN_START);
      }
      onError('Unrecognized message', parsedMessage);
   }
}

function start() {
   console.log("Starting video call ...")
   // Disable start button
   setState(I_AM_STARTING);
   showSpinner(videoInput, videoOutput);

   console.log("Creating WebRtcPeer and generating local sdp offer ...");

   var options = {
      localVideo : videoInput,
      remoteVideo : videoOutput,
      onicecandidate : onIceCandidate
   }
   webRtcPeer = new kurentoUtils.WebRtcPeer.WebRtcPeerSendrecv(options,
         function(error) {
            if (error) {
               return console.error(error);
            }
            webRtcPeer.generateOffer(onOffer);
         });
}

function onOffer(error, offerSdp) {
   if (error)
      return console.error("Error generating the offer");
   console.info('Invoking SDP offer callback function ' + location.host);
   var message = {
      id : 'start',
      sdpOffer : offerSdp
   }
   sendMessage(message);
}

function onError(error) {
   console.error(error);
}

function onIceCandidate(candidate) {
   console.log("Local candidate" + JSON.stringify(candidate));

   var message = {
      id : 'onIceCandidate',
      candidate : candidate
   };
   sendMessage(message);
}

function startResponse(message) {
   setState(I_CAN_STOP);
   console.log("SDP answer received from server. Processing ...");

   webRtcPeer.processAnswer(message.sdpAnswer, function(error) {
      if (error)
         return console.error(error);
   });
}

function stop() {
   console.log("Stopping video call ...");
   setState(I_CAN_START);
   if (webRtcPeer) {
      webRtcPeer.dispose();
      webRtcPeer = null;

      var message = {
         id : 'stop'
      }
      sendMessage(message);
   }
   hideSpinner(videoInput, videoOutput);
}

function sendMessage(message) {
   var jsonMessage = JSON.stringify(message);
   console.log('Senging message: ' + jsonMessage);
   ws.send(jsonMessage);
}
Dependencies

This Java Spring application is implemented using Maven. The relevant part of the pom.xml is where Kurento dependencies are declared. As the following snippet shows, we need two dependencies: the Kurento Client Java dependency (kurento-client) and the JavaScript Kurento utility library (kurento-utils) for the client-side. Other client libraries are managed with webjars:

<dependencies>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-client</artifactId>
   </dependency>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-utils-js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars</groupId>
      <artifactId>webjars-locator</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>bootstrap</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>demo-console</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>adapter.js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>jquery</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>ekko-lightbox</artifactId>
   </dependency>
</dependencies>

注解

We are in active development. You can find the latest version of Kurento Java Client at Maven Central.

Kurento Java Client has a minimum requirement of Java 7. Hence, you need to include the following properties in your pom:

<maven.compiler.target>1.7</maven.compiler.target>
<maven.compiler.source>1.7</maven.compiler.source>

Play media to WebRTC

This tutorial reads a file from disk and plays the video to WebRTC.

Java - Player

This tutorial opens a URL and plays its content to WebRTC where it is possible to choose if it plays video and audio, only video or only audio.

注解

This tutorial has been configured to use https. Follow the instructions to secure your application.

For the impatient: running this example

You need to have installed the Kurento Media Server before running this example. Read the installation guide for further information.

To launch the application, you need to clone the GitHub project where this demo is hosted, and then run the main class:

git clone https://github.com/Kurento/kurento-tutorial-java.git
cd kurento-tutorial-java/kurento-player
git checkout 6.6.2
mvn compile exec:java

Access the application connecting to the URL https://localhost:8443/ in a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the flag kms.url to the JVM executing the demo. As we’ll be using maven, you should execute the following command

mvn compile exec:java -Dkms.url=ws://kms_host:kms_port/kurento
Understanding this example

To implement this behavior we have to create a Media Pipeline composed by one PlayerEndpoint and one WebRtcEndpoint. The PlayerEnpdoint plays a video and WebRtcEndpoint shows it.

This is a web application, and therefore it follows a client-server architecture. At the client-side, the logic is implemented in JavaScript. At the server-side, we use a Spring-Boot based server application consuming the Kurento Java Client API, to control Kurento Media Server capabilities. All in all, the high level architecture of this demo is three-tier. To communicate these entities, two WebSockets are used. First, a WebSocket is created between client and application server to implement a custom signaling protocol. Second, another WebSocket is used to perform the communication between the Kurento Java Client and the Kurento Media Server. This communication takes place using the Kurento Protocol. For further information on it, please see this page of the documentation.

The following sections analyze in depth the server (Java) and client-side (JavaScript) code of this application. The complete source code can be found in GitHub.

Application Server Logic

This demo has been developed using Java in the server-side, based on the Spring Boot framework, which embeds a Tomcat web server within the generated maven artifact, and thus simplifies the development and deployment process.

注解

You can use whatever Java server side technology you prefer to build web applications with Kurento. For example, a pure Java EE application, SIP Servlets, Play, Vert.x, etc. Here we chose Spring Boot for convenience.

The main class of this demo is PlayerApp. As you can see, the KurentoClient is instantiated in this class as a Spring Bean. This bean is used to create Kurento Media Pipelines, which are used to add media capabilities to the application. In this instantiation we see that we need to specify to the client library the location of the Kurento Media Server. In this example, we assume it’s located at localhost listening in port 8888. If you reproduce this example you’ll need to insert the specific location of your Kurento Media Server instance there.

Once the Kurento Client has been instantiated, you are ready for communicating with Kurento Media Server and controlling its multimedia capabilities.

@EnableWebSocket
@SpringBootApplication
public class PlayerApp implements WebSocketConfigurer {

  private static final String KMS_WS_URI_PROP = "kms.url";
  private static final String KMS_WS_URI_DEFAULT = "ws://localhost:8888/kurento";

  @Bean
  public PlayerHandler handler() {
    return new PlayerHandler();
  }

  @Bean
  public KurentoClient kurentoClient() {
    return KurentoClient.create(System.getProperty(KMS_WS_URI_PROP, KMS_WS_URI_DEFAULT));
  }

  @Override
  public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
    registry.addHandler(handler(), "/player");
  }

  public static void main(String[] args) throws Exception {
    new SpringApplication(PlayerApp.class).run(args);
  }
}

This web application follows a Single Page Application architecture (SPA), and uses a WebSocket to communicate client with application server by means of requests and responses. Specifically, the main app class implements the interface WebSocketConfigurer to register a WebSocketHanlder to process WebSocket requests in the path /player.

PlayerHandler class implements TextWebSocketHandler to handle text WebSocket requests. The central piece of this class is the method handleTextMessage. This method implements the actions for requests, returning responses through the WebSocket. In other words, it implements the server part of the signaling protocol depicted in the previous sequence diagram.

In the designed protocol, there are seven different kinds of incoming messages to the Server : start, stop, pause, resume, doSeek, getPosition and onIceCandidates. These messages are treated in the switch clause, taking the proper steps in each case.

public class PlayerHandler extends TextWebSocketHandler {

  @Autowired
  private KurentoClient kurento;

  private final Logger log = LoggerFactory.getLogger(PlayerHandler.class);
  private final Gson gson = new GsonBuilder().create();
  private final ConcurrentHashMap<String, PlayerMediaPipeline> pipelines =
      new ConcurrentHashMap<>();

  @Override
  public void handleTextMessage(WebSocketSession session, TextMessage message) throws Exception {
    JsonObject jsonMessage = gson.fromJson(message.getPayload(), JsonObject.class);
    String sessionId = session.getId();
    log.debug("Incoming message {} from sessionId", jsonMessage, sessionId);

    try {
      switch (jsonMessage.get("id").getAsString()) {
        case "start":
          start(session, jsonMessage);
          break;
        case "stop":
          stop(sessionId);
          break;
        case "pause":
          pause(sessionId);
          break;
        case "resume":
          resume(session);
          break;
        case "doSeek":
          doSeek(session, jsonMessage);
          break;
        case "getPosition":
          getPosition(session);
          break;
        case "onIceCandidate":
          onIceCandidate(sessionId, jsonMessage);
          break;
        default:
          sendError(session, "Invalid message with id " + jsonMessage.get("id").getAsString());
          break;
      }
    } catch (Throwable t) {
      log.error("Exception handling message {} in sessionId {}", jsonMessage, sessionId, t);
      sendError(session, t.getMessage());
    }
  }


  private void start(final WebSocketSession session, JsonObject jsonMessage) {
    ...
  }

  private void pause(String sessionId) {
   ...
  }

  private void resume(final WebSocketSession session) {
  ...
  }

  private void doSeek(final WebSocketSession session, JsonObject jsonMessage) {
  ...
  }

  private void getPosition(final WebSocketSession session) {
  ...
  }

  private void stop(String sessionId) {
  ...
  }

  private void sendError(WebSocketSession session, String message) {
    ...
  }
}

In the following snippet, we can see the start method. It handles the ICE candidates gathering, creates a Media Pipeline, creates the Media Elements (WebRtcEndpoint and PlayerEndpoint) and makes the connections between them and plays the video. A startResponse message is sent back to the client with the SDP answer. When the MediaConnected event is received, info about the video is retrieved and sent back to the client in a videoInfo message.

private void start(final WebSocketSession session, JsonObject jsonMessage) {
  final UserSession user = new UserSession(); MediaPipeline pipeline =
  kurento.createMediaPipeline(); user.setMediaPipeline(pipeline);
  WebRtcEndpoint webRtcEndpoint = new
  WebRtcEndpoint.Builder(pipeline).build();
  user.setWebRtcEndpoint(webRtcEndpoint); String videourl =
  jsonMessage.get("videourl").getAsString(); final PlayerEndpoint
  playerEndpoint = new PlayerEndpoint.Builder(pipeline, videourl).build();
  user.setPlayerEndpoint(playerEndpoint); users.put(session.getId(), user);

  playerEndpoint.connect(webRtcEndpoint);

  // 2. WebRtcEndpoint // ICE candidates
  webRtcEndpoint.addIceCandidateFoundListener(new
  EventListener<IceCandidateFoundEvent>() {
    @Override public void onEvent(IceCandidateFoundEvent event) {
      JsonObject response = new JsonObject();
      response.addProperty("id", "iceCandidate"); response.add("candidate",
      JsonUtils.toJsonObject(event.getCandidate())); try {
        synchronized (session) {
          session.sendMessage(new
          TextMessage(response.toString()));
        }
      } catch (IOException e) {
        log.debug(e.getMessage());
      }
    }
  });

  String sdpOffer = jsonMessage.get("sdpOffer").getAsString(); String
  sdpAnswer = webRtcEndpoint.processOffer(sdpOffer);

  JsonObject response = new JsonObject(); response.addProperty("id",
  "startResponse"); response.addProperty("sdpAnswer", sdpAnswer);
  sendMessage(session, response.toString());

  webRtcEndpoint.addMediaStateChangedListener(new
  EventListener<MediaStateChangedEvent>() {
    @Override public void onEvent(MediaStateChangedEvent event) {

      if (event.getNewState() == MediaState.CONNECTED) {
        VideoInfo videoInfo = playerEndpoint.getVideoInfo();

        JsonObject response = new JsonObject();
        response.addProperty("id", "videoInfo");
        response.addProperty("isSeekable", videoInfo.getIsSeekable());
        response.addProperty("initSeekable", videoInfo.getSeekableInit());
        response.addProperty("endSeekable", videoInfo.getSeekableEnd());
        response.addProperty("videoDuration", videoInfo.getDuration());
        sendMessage(session, response.toString());
      }
    }
  });

  webRtcEndpoint.gatherCandidates();

  // 3. PlayEndpoint playerEndpoint.addErrorListener(new
  EventListener<ErrorEvent>() {
    @Override public void onEvent(ErrorEvent event) {
      log.info("ErrorEvent: {}", event.getDescription());
      sendPlayEnd(session);
    }
  });

  playerEndpoint.addEndOfStreamListener(new
  EventListener<EndOfStreamEvent>() {
    @Override public void onEvent(EndOfStreamEvent event) {
      log.info("EndOfStreamEvent: {}", event.getTimestamp());
      sendPlayEnd(session);
    }
  });

  playerEndpoint.play();
}

The pause method retrieves the user associated to the current session, and invokes the pause method on the PlayerEndpoint.

private void pause(String sessionId) {
  UserSession user = users.get(sessionId);

  if (user != null) {
    user.getPlayerEndpoint().pause();
  }
}

The resume method starts the PlayerEndpoint of the current user, sending back the information about the video, so the client side can refresh the stats.

private void resume(String sessionId) {
  UserSession user = users.get(session.getId());

  if (user != null) {
    user.getPlayerEndpoint().play(); VideoInfo videoInfo =
    user.getPlayerEndpoint().getVideoInfo();

    JsonObject response = new JsonObject(); response.addProperty("id",
    "videoInfo"); response.addProperty("isSeekable",
    videoInfo.getIsSeekable()); response.addProperty("initSeekable",
    videoInfo.getSeekableInit()); response.addProperty("endSeekable",
    videoInfo.getSeekableEnd()); response.addProperty("videoDuration",
    videoInfo.getDuration()); sendMessage(session, response.toString());
  }
}

The doSeek method gets the user by sessionId, and calls the method setPosition of the PlayerEndpoint with the new playing position. A seek message is sent back to the client if the seek fails.

private void doSeek(final WebSocketSession session, JsonObject jsonMessage) {
  UserSession user = users.get(session.getId());

  if (user != null) {
    try {
      user.getPlayerEndpoint().setPosition(jsonMessage.get("position").getAsLong());
    } catch (KurentoException e) {
      log.debug("The seek cannot be performed"); JsonObject response =
      new JsonObject(); response.addProperty("id", "seek");
      response.addProperty("message", "Seek failed"); sendMessage(session,
      response.toString());
    }
  }
}

The getPosition calls the method getPosition of the PlayerEndpoint of the current user. A position message is sent back to the client with the actual position of the video.

private void getPosition(final WebSocketSession session) {
  UserSession user = users.get(session.getId());

  if (user != null) {
    long position = user.getPlayerEndpoint().getPosition();

    JsonObject response = new JsonObject(); response.addProperty("id",
    "position"); response.addProperty("position", position);
    sendMessage(session, response.toString());
  }
}

The stop method is quite simple: it searches the user by sessionId and stops the PlayerEndpoint. Finally, it releases the media elements and removes the user from the list of active users.

private void stop(String sessionId) {
  UserSession user = users.remove(sessionId);

  if (user != null) {
    user.release();
  }
}

The sendError method is quite simple: it sends an error message to the client when an exception is caught in the server-side.

private void sendError(WebSocketSession session, String message) {
  try {
    JsonObject response = new JsonObject(); response.addProperty("id",
    "error"); response.addProperty("message", message);
    session.sendMessage(new TextMessage(response.toString()));
  } catch (IOException e) {
    log.error("Exception sending message", e);
  }
}
Client-Side Logic

Let’s move now to the client-side of the application. To call the previously created WebSocket service in the server-side, we use the JavaScript class WebSocket. We use a specific Kurento JavaScript library called kurento-utils.js to simplify the WebRTC interaction with the server. This library depends on adapter.js, which is a JavaScript WebRTC utility maintained by Google that abstracts away browser differences. Finally jquery.js is also needed in this application.

These libraries are linked in the index.html web page, and are used in the index.js. In the following snippet we can see the creation of the WebSocket (variable ws) in the path /player. Then, the onmessage listener of the WebSocket is used to implement the JSON signaling protocol in the client-side. Notice that there are seven incoming messages to client: startResponse, playEnd, error, videoInfo, seek, position and iceCandidate. Convenient actions are taken to implement each step in the communication. For example, in functions start the function WebRtcPeer.WebRtcPeerSendrecv of kurento-utils.js is used to start a WebRTC communication.

var ws = new WebSocket('wss://' + location.host + '/player');

ws.onmessage = function(message) {
   var parsedMessage = JSON.parse(message.data);
   console.info('Received message: ' + message.data);

   switch (parsedMessage.id) {
   case 'startResponse':
      startResponse(parsedMessage);
      break;
   case 'error':
      if (state == I_AM_STARTING) {
         setState(I_CAN_START);
      }
      onError('Error message from server: ' + parsedMessage.message);
      break;
   case 'playEnd':
      playEnd();
      break;
     break;
   case 'videoInfo':
      showVideoData(parsedMessage);
      break;
   case 'iceCandidate':
      webRtcPeer.addIceCandidate(parsedMessage.candidate, function(error) {
         if (error)
            return console.error('Error adding candidate: ' + error);
      });
      break;
   case 'seek':
      console.log (parsedMessage.message);
      break;
   case 'position':
      document.getElementById("videoPosition").value = parsedMessage.position;
      break;
   default:
      if (state == I_AM_STARTING) {
         setState(I_CAN_START);
      }
      onError('Unrecognized message', parsedMessage);
   }
}

function start() {
   // Disable start button
   setState(I_AM_STARTING);
   showSpinner(video);

   var mode = $('input[name="mode"]:checked').val();
   console
         .log('Creating WebRtcPeer in " + mode + " mode and generating local sdp offer ...');

   // Video and audio by default
   var userMediaConstraints = {
      audio : true,
      video : true
   }

   if (mode == 'video-only') {
      userMediaConstraints.audio = false;
   } else if (mode == 'audio-only') {
      userMediaConstraints.video = false;
   }

   var options = {
      remoteVideo : video,
      mediaConstraints : userMediaConstraints,
      onicecandidate : onIceCandidate
   }

   console.info('User media constraints' + userMediaConstraints);

   webRtcPeer = new kurentoUtils.WebRtcPeer.WebRtcPeerRecvonly(options,
         function(error) {
            if (error)
               return console.error(error);
            webRtcPeer.generateOffer(onOffer);
         });
}

function onOffer(error, offerSdp) {
   if (error)
      return console.error('Error generating the offer');
   console.info('Invoking SDP offer callback function ' + location.host);

   var message = {
      id : 'start',
      sdpOffer : offerSdp,
      videourl : document.getElementById('videourl').value
   }
   sendMessage(message);
}

function onError(error) {
   console.error(error);
}

function onIceCandidate(candidate) {
   console.log('Local candidate' + JSON.stringify(candidate));

   var message = {
      id : 'onIceCandidate',
      candidate : candidate
   }
   sendMessage(message);
}

function startResponse(message) {
   setState(I_CAN_STOP);
   console.log('SDP answer received from server. Processing ...');

   webRtcPeer.processAnswer(message.sdpAnswer, function(error) {
      if (error)
         return console.error(error);
   });
}

function pause() {
   togglePause()
   console.log('Pausing video ...');
   var message = {
      id : 'pause'
   }
   sendMessage(message);
}

function resume() {
   togglePause()
   console.log('Resuming video ...');
   var message = {
      id : 'resume'
   }
   sendMessage(message);
}

function stop() {
   console.log('Stopping video ...');
   setState(I_CAN_START);
   if (webRtcPeer) {
      webRtcPeer.dispose();
      webRtcPeer = null;

      var message = {
         id : 'stop'
      }
      sendMessage(message);
   }
   hideSpinner(video);
}

function playEnd() {
   setState(I_CAN_START);
   hideSpinner(video);
}

function doSeek() {
   var message = {
     id : 'doSeek',
     position: document.getElementById("seekPosition").value
   }
   sendMessage(message);
 }

 function getPosition() {
   var message = {
     id : 'getPosition'
   }
   sendMessage(message);
 }

 function showVideoData(parsedMessage) {
   //Show video info
   isSeekable = parsedMessage.isSeekable;
   if (isSeekable) {
       document.getElementById('isSeekable').value = "true";
       enableButton('#doSeek', 'doSeek()');
     } else {
       document.getElementById('isSeekable').value = "false";
     }

     document.getElementById('initSeek').value = parsedMessage.initSeekable;
     document.getElementById('endSeek').value = parsedMessage.endSeekable;
     document.getElementById('duration').value = parsedMessage.videoDuration;

     enableButton('#getPosition', 'getPosition()');
 }

function sendMessage(message) {
   var jsonMessage = JSON.stringify(message);
   console.log('Senging message: ' + jsonMessage);
   ws.send(jsonMessage);
}
Dependencies

This Java Spring application is implemented using Maven. The relevant part of the pom.xml is where Kurento dependencies are declared. As the following snippet shows, we need two dependencies: the Kurento Client Java dependency (kurento-client) and the JavaScript Kurento utility library (kurento-utils) for the client-side. Other client libraries are managed with webjars:

<dependencies>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-client</artifactId>
   </dependency>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-utils-js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars</groupId>
      <artifactId>webjars-locator</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>bootstrap</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>demo-console</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>adapter.js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>jquery</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>ekko-lightbox</artifactId>
   </dependency>
</dependencies>

注解

We are in active development. You can find the latest version of Kurento Java Client at Maven Central.

Kurento Java Client has a minimum requirement of Java 7. Hence, you need to include the following properties in your pom:

<maven.compiler.target>1.7</maven.compiler.target>
<maven.compiler.source>1.7</maven.compiler.source>

WebRTC outgoing data channels

This tutorial injects video to a QR filter and then sends the stream to WebRTC. QR detection events are delivered by means of WebRTC data channels, to be displayed in browser.

Java - Send DataChannel

This tutorial connects a player with a QR code detection filter and sends output to WebRTC. Code detection events are sent to browser using WebRTC datachannels.

注解

This tutorial has been configured to use https. Follow the instructions to secure your application.

For the impatient: running this example

You need to have installed the Kurento Media Server before running this example. Read the installation guide for further information.

To launch the application, you need to clone the GitHub project where this demo is hosted, and then run the main class:

git clone https://github.com/Kurento/kurento-tutorial-java.git
cd kurento-tutorial-java/kurento-send-data-channel
git checkout 6.6.2
mvn compile exec:java

Access the application connecting to the URL https://localhost:8443/ in a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the flag kms.url to the JVM executing the demo. As we’ll be using maven, you should execute the following command

mvn compile exec:java -Dkms.url=ws://kms_host:kms_port/kurento

注解

This demo needs the kms-datachannelexample module installed in the media server. That module is available in the Kurento repositories, so it is possible to install it with:

sudo apt-get install kms-datachannelexample
Understanding this example

To implement this behavior we have to create a Media Pipeline composed by one PlayerEndpoint, one KmsSendData and one WebRtcEndpoint. The PlayerEnpdoint plays a video and it detects QR codes into the images. The info about detected codes is sent through data channels (KmsSendData) from the Kurento media server to the browser (WebRtcEndpoint). The browser shows the info in a text form.

This is a web application, and therefore it follows a client-server architecture. At the client-side, the logic is implemented in JavaScript. At the server-side, we use a Spring-Boot based server application consuming the Kurento Java Client API, to control Kurento Media Server capabilities. All in all, the high level architecture of this demo is three-tier. To communicate these entities, two WebSockets are used. First, a WebSocket is created between client and application server to implement a custom signaling protocol. Second, another WebSocket is used to perform the communication between the Kurento Java Client and the Kurento Media Server. This communication takes place using the Kurento Protocol. For further information on it, please see this page of the documentation.

The following sections analyze in depth the server (Java) and client-side (JavaScript) code of this application. The complete source code can be found in GitHub.

Application Server Logic

This demo has been developed using Java in the server-side, based on the Spring Boot framework, which embeds a Tomcat web server within the generated maven artifact, and thus simplifies the development and deployment process.

注解

You can use whatever Java server side technology you prefer to build web applications with Kurento. For example, a pure Java EE application, SIP Servlets, Play, Vert.x, etc. Here we chose Spring Boot for convenience.

The main class of this demo is SendDataChannelApp. As you can see, the KurentoClient is instantiated in this class as a Spring Bean. This bean is used to create Kurento Media Pipelines, which are used to add media capabilities to the application. In this instantiation we see that we need to specify to the client library the location of the Kurento Media Server. In this example, we assume it is located at localhost listening in port 8888. If you reproduce this example you’ll need to insert the specific location of your Kurento Media Server instance there.

Once the Kurento Client has been instantiated, you are ready for communicating with Kurento Media Server and controlling its multimedia capabilities.

@EnableWebSocket
@SpringBootApplication
public class SendDataChannelApp implements WebSocketConfigurer {

  static final String DEFAULT_APP_SERVER_URL = "https://localhost:8443";

  @Bean
  public SendDataChannelHandler handler() {
    return new SendDataChannelHandler();
  }

  @Bean
  public KurentoClient kurentoClient() {
    return KurentoClient.create();
  }

  @Override
  public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
    registry.addHandler(handler(), "/senddatachannel");
  }

  public static void main(String[] args) throws Exception {
    new SpringApplication(SendDataChannelApp.class).run(args);
  }
}

This web application follows a Single Page Application architecture (SPA), and uses a WebSocket to communicate client with application server by means of requests and responses. Specifically, the main app class implements the interface WebSocketConfigurer to register a WebSocketHanlder to process WebSocket requests in the path /senddatachannel.

SendDataChannelHandler class implements TextWebSocketHandler to handle text WebSocket requests. The central piece of this class is the method handleTextMessage. This method implements the actions for requests, returning responses through the WebSocket. In other words, it implements the server part of the signaling protocol depicted in the previous sequence diagram.

In the designed protocol there are three different kinds of incoming messages to the Server : start, stop and onIceCandidates. These messages are treated in the switch clause, taking the proper steps in each case.

public class SendDataChannelHandler extends TextWebSocketHandler {

  private final Logger log = LoggerFactory.getLogger(SendDataChannelHandler.class);
  private static final Gson gson = new GsonBuilder().create();

  private final ConcurrentHashMap<String, UserSession> users = new ConcurrentHashMap<>();

  @Autowired
  private KurentoClient kurento;

  @Override
  public void handleTextMessage(WebSocketSession session, TextMessage message) throws Exception {
    JsonObject jsonMessage = gson.fromJson(message.getPayload(), JsonObject.class);

    log.debug("Incoming message: {}", jsonMessage);

    switch (jsonMessage.get("id").getAsString()) {
      case "start":
        start(session, jsonMessage);
        break;
      case "stop": {
        UserSession user = users.remove(session.getId());
        if (user != null) {
          user.release();
        }
        break;
      }
      case "onIceCandidate": {
        JsonObject jsonCandidate = jsonMessage.get("candidate").getAsJsonObject();

        UserSession user = users.get(session.getId());
        if (user != null) {
          IceCandidate candidate = new IceCandidate(jsonCandidate.get("candidate").getAsString(),
              jsonCandidate.get("sdpMid").getAsString(),
              jsonCandidate.get("sdpMLineIndex").getAsInt());
          user.addCandidate(candidate);
        }
        break;
      }
      default:
        sendError(session, "Invalid message with id " + jsonMessage.get("id").getAsString());
        break;
    }
  }

  private void start(final WebSocketSession session, JsonObject jsonMessage) {
    ...
  }

  private void sendError(WebSocketSession session, String message) {
    ...
  }
}

In the following snippet, we can see the start method. It handles the ICE candidates gathering, creates a Media Pipeline, creates the Media Elements (WebRtcEndpoint, KmsSendData and PlayerEndpoint) and make the connections among them. A startResponse message is sent back to the client with the SDP answer.

private void start(final WebSocketSession session, JsonObject jsonMessage) {
   try {
      // User session
      UserSession user = new UserSession();
      MediaPipeline pipeline = kurento.createMediaPipeline();
      user.setMediaPipeline(pipeline);
      WebRtcEndpoint webRtcEndpoint = new WebRtcEndpoint.Builder(pipeline).useDataChannels()
          .build();
      user.setWebRtcEndpoint(webRtcEndpoint);
      PlayerEndpoint player = new PlayerEndpoint.Builder(pipeline,
          "http://files.kurento.org/video/filter/barcodes.webm").build();
      user.setPlayer(player);
      users.put(session.getId(), user);

      // ICE candidates
      webRtcEndpoint.addIceCandidateFoundListener(new EventListener<IceCandidateFoundEvent>() {
        @Override
        public void onEvent(IceCandidateFoundEvent event) {
          JsonObject response = new JsonObject();
          response.addProperty("id", "iceCandidate");
          response.add("candidate", JsonUtils.toJsonObject(event.getCandidate()));
          try {
            synchronized (session) {
              session.sendMessage(new TextMessage(response.toString()));
            }
          } catch (IOException e) {
            log.debug(e.getMessage());
          }
        }
      });

      // Media logic
      KmsSendData kmsSendData = new KmsSendData.Builder(pipeline).build();

      player.connect(kmsSendData);
      kmsSendData.connect(webRtcEndpoint);

      // SDP negotiation (offer and answer)
      String sdpOffer = jsonMessage.get("sdpOffer").getAsString();
      String sdpAnswer = webRtcEndpoint.processOffer(sdpOffer);

      JsonObject response = new JsonObject();
      response.addProperty("id", "startResponse");
      response.addProperty("sdpAnswer", sdpAnswer);

      synchronized (session) {
        session.sendMessage(new TextMessage(response.toString()));
      }

      webRtcEndpoint.gatherCandidates();
      player.play();

    } catch (Throwable t) {
      sendError(session, t.getMessage());
    }
}

The sendError method is quite simple: it sends an error message to the client when an exception is caught in the server-side.

private void sendError(WebSocketSession session, String message) {
   try {
      JsonObject response = new JsonObject();
      response.addProperty("id", "error");
      response.addProperty("message", message);
      session.sendMessage(new TextMessage(response.toString()));
   } catch (IOException e) {
      log.error("Exception sending message", e);
   }
}
Client-Side Logic

Let’s move now to the client-side of the application. To call the previously created WebSocket service in the server-side, we use the JavaScript class WebSocket. We use a specific Kurento JavaScript library called kurento-utils.js to simplify the WebRTC interaction with the server. This library depends on adapter.js, which is a JavaScript WebRTC utility maintained by Google that abstracts away browser differences. Finally jquery.js is also needed in this application.

These libraries are linked in the index.html web page, and are used in the index.js. In the following snippet we can see the creation of the WebSocket (variable ws) in the path /senddatachannel. Then, the onmessage listener of the WebSocket is used to implement the JSON signaling protocol in the client-side. Notice that there are three incoming messages to client: startResponse, error, and iceCandidate. Convenient actions are taken to implement each step in the communication. For example, in functions start the function WebRtcPeer.WebRtcPeerSendrecv of kurento-utils.js is used to start a WebRTC communication.

var ws = new WebSocket('wss://' + location.host + '/senddatachannel');

ws.onmessage = function(message) {
   var parsedMessage = JSON.parse(message.data);
   console.info('Received message: ' + message.data);

   switch (parsedMessage.id) {
   case 'startResponse':
      startResponse(parsedMessage);
      break;
   case 'error':
      if (state == I_AM_STARTING) {
         setState(I_CAN_START);
      }
      onError("Error message from server: " + parsedMessage.message);
      break;
   case 'iceCandidate':
      webRtcPeer.addIceCandidate(parsedMessage.candidate, function(error) {
         if (error) {
            console.error("Error adding candidate: " + error);
            return;
         }
      });
      break;
   default:
      if (state == I_AM_STARTING) {
         setState(I_CAN_START);
      }
      onError('Unrecognized message', parsedMessage);
   }
}

function start() {
   console.log("Starting video call ...")
   // Disable start button
   setState(I_AM_STARTING);
   showSpinner(videoOutput);

   var servers = null;
    var configuration = null;
    var peerConnection = new RTCPeerConnection(servers, configuration);

    console.log("Creating channel");
    var dataConstraints = null;

    channel = peerConnection.createDataChannel(getChannelName (), dataConstraints);

    channel.onmessage = onMessage;

    var dataChannelReceive = document.getElementById('dataChannelReceive');

    function onMessage (event) {
      console.log("Received data " + event["data"]);
      dataChannelReceive.value = event["data"];
    }

      console.log("Creating WebRtcPeer and generating local sdp offer ...");

   var options = {
      peerConnection: peerConnection,
      remoteVideo : videoOutput,
      onicecandidate : onIceCandidate
   }
   webRtcPeer = new kurentoUtils.WebRtcPeer.WebRtcPeerRecvonly(options,
         function(error) {
            if (error) {
               return console.error(error);
            }
            webRtcPeer.generateOffer(onOffer);
         });
}

function closeChannels(){

   if(channel){
     channel.close();
     $('#dataChannelSend').disabled = true;
     $('#send').attr('disabled', true);
     channel = null;
   }
}

function onOffer(error, offerSdp) {
   if (error)
      return console.error("Error generating the offer");
   console.info('Invoking SDP offer callback function ' + location.host);
   var message = {
      id : 'start',
      sdpOffer : offerSdp
   }
   sendMessage(message);
}

function onError(error) {
   console.error(error);
}

function onIceCandidate(candidate) {
   console.log("Local candidate" + JSON.stringify(candidate));

   var message = {
      id : 'onIceCandidate',
      candidate : candidate
   };
   sendMessage(message);
}

function startResponse(message) {
   setState(I_CAN_STOP);
   console.log("SDP answer received from server. Processing ...");

   webRtcPeer.processAnswer(message.sdpAnswer, function(error) {
      if (error)
         return console.error(error);
   });
}

function stop() {
   console.log("Stopping video call ...");
   setState(I_CAN_START);
   if (webRtcPeer) {
       closeChannels();

      webRtcPeer.dispose();
      webRtcPeer = null;

      var message = {
         id : 'stop'
      }
      sendMessage(message);
   }
   hideSpinner(videoOutput);
}

function sendMessage(message) {
   var jsonMessage = JSON.stringify(message);
   console.log('Senging message: ' + jsonMessage);
   ws.send(jsonMessage);
}
Dependencies

This Java Spring application is implemented using Maven. The relevant part of the pom.xml is where Kurento dependencies are declared. As the following snippet shows, we need two dependencies: the Kurento Client Java dependency (kurento-client) and the JavaScript Kurento utility library (kurento-utils) for the client-side. Other client libraries are managed with webjars:

<dependencies>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-client</artifactId>
   </dependency>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-utils-js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars</groupId>
      <artifactId>webjars-locator</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>bootstrap</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>demo-console</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>adapter.js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>jquery</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>ekko-lightbox</artifactId>
   </dependency>
</dependencies>

注解

We are in active development. You can find the latest version of Kurento Java Client at Maven Central.

Kurento Java Client has a minimum requirement of Java 7. Hence, you need to include the following properties in your pom:

<maven.compiler.target>1.7</maven.compiler.target>
<maven.compiler.source>1.7</maven.compiler.source>

WebRTC incoming data channel

This tutorial shows how text messages sent from browser can be delivered by data channels, to be displayed together with loopback video.

Java - Show DataChannel

This demo allows sending text from browser to the media server through data channels. That text will be shown in the loopback video.

注解

This tutorial has been configured to use https. Follow the instructions to secure your application.

For the impatient: running this example

You need to have installed the Kurento Media Server before running this example. Read the installation guide for further information.

To launch the application, you need to clone the GitHub project where this demo is hosted, and then run the main class:

git clone https://github.com/Kurento/kurento-tutorial-java.git
cd kurento-tutorial-java/kurento-show-data-channel
git checkout 6.6.2
mvn compile exec:java

Access the application connecting to the URL https://localhost:8443/ in a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the flag kms.url to the JVM executing the demo. As we’ll be using maven, you should execute the following command

mvn compile exec:java -Dkms.url=ws://kms_host:kms_port/kurento

注解

This demo needs the kms-datachannelexample module installed in the media server. That module is available in the Kurento repositories, so it is possible to install it with:

sudo apt-get install kms-datachannelexample
Understanding this example

This tutorial creates a Media Pipeline consisting of media elements: WebRtcEndpoint and KmsSendData. Any text inserted in the textbox is sent from Kurento Media Server (KmsSendData) back to browser (WebRtcEndpoint) and shown with loopback video.

This is a web application, and therefore it follows a client-server architecture. At the client-side, the logic is implemented in JavaScript. At the server-side, we use a Spring-Boot based server application consuming the Kurento Java Client API, to control Kurento Media Server capabilities. All in all, the high level architecture of this demo is three-tier. To communicate these entities, two WebSockets are used. First, a WebSocket is created between client and application server to implement a custom signaling protocol. Second, another WebSocket is used to perform the communication between the Kurento Java Client and the Kurento Media Server. This communication takes place using the Kurento Protocol. For further information on it, please see this page of the documentation.

The following sections analyze in depth the server (Java) and client-side (JavaScript) code of this application. The complete source code can be found in GitHub.

Application Server Logic

This demo has been developed using Java in the server-side, based on the Spring Boot framework, which embeds a Tomcat web server within the generated maven artifact, and thus simplifies the development and deployment process.

注解

You can use whatever Java server side technology you prefer to build web applications with Kurento. For example, a pure Java EE application, SIP Servlets, Play, Vert.x, etc. Here we chose Spring Boot for convenience.

The main class of this demo is ShowDataChannelApp. As you can see, the KurentoClient is instantiated in this class as a Spring Bean. This bean is used to create Kurento Media Pipelines, which are used to add media capabilities to the application. In this instantiation we see that we need to specify to the client library the location of the Kurento Media Server. In this example, we assume it’s located at localhost listening in port 8888. If you reproduce this example you’ll need to insert the specific location of your Kurento Media Server instance there.

Once the Kurento Client has been instantiated, you are ready for communicating with Kurento Media Server and controlling its multimedia capabilities.

@EnableWebSocket
@SpringBootApplication
public class ShowDataChannelApp implements WebSocketConfigurer {

  static final String DEFAULT_APP_SERVER_URL = "https://localhost:8443";

  @Bean
  public ShowDataChannelHandler handler() {
    return new ShowDataChannelHandler();
  }

  @Bean
  public KurentoClient kurentoClient() {
    return KurentoClient.create();
  }

  @Override
  public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
    registry.addHandler(handler(), "/showdatachannel");
  }

  public static void main(String[] args) throws Exception {
    new SpringApplication(ShowDataChannelApp.class).run(args);
  }
}

This web application follows a Single Page Application architecture (SPA), and uses a WebSocket to communicate client with application server by means of requests and responses. Specifically, the main app class implements the interface WebSocketConfigurer to register a WebSocketHanlder to process WebSocket requests in the path /showdatachannel.

ShowDataChannelHandler class implements TextWebSocketHandler to handle text WebSocket requests. The central piece of this class is the method handleTextMessage. This method implements the actions for requests, returning responses through the WebSocket. In other words, it implements the server part of the signaling protocol depicted in the previous sequence diagram.

In the designed protocol there are three different kinds of incoming messages to the Server : start, stop and onIceCandidates. These messages are treated in the switch clause, taking the proper steps in each case.

public class ShowDataChannelHandler extends TextWebSocketHandler {

  private final Logger log = LoggerFactory.getLogger(ShowDataChannelHandler.class);
  private static final Gson gson = new GsonBuilder().create();

  private final ConcurrentHashMap<String, UserSession> users = new ConcurrentHashMap<>();

  @Autowired
  private KurentoClient kurento;

  @Override
  public void handleTextMessage(WebSocketSession session, TextMessage message) throws Exception {
    JsonObject jsonMessage = gson.fromJson(message.getPayload(), JsonObject.class);

    log.debug("Incoming message: {}", jsonMessage);

    switch (jsonMessage.get("id").getAsString()) {
      case "start":
        start(session, jsonMessage);
        break;
      case "stop": {
        UserSession user = users.remove(session.getId());
        if (user != null) {
          user.release();
        }
        break;
      }
      case "onIceCandidate": {
        JsonObject jsonCandidate = jsonMessage.get("candidate").getAsJsonObject();

        UserSession user = users.get(session.getId());
        if (user != null) {
          IceCandidate candidate = new IceCandidate(jsonCandidate.get("candidate").getAsString(),
              jsonCandidate.get("sdpMid").getAsString(),
              jsonCandidate.get("sdpMLineIndex").getAsInt());
          user.addCandidate(candidate);
        }
        break;
      }
      default:
        sendError(session, "Invalid message with id " + jsonMessage.get("id").getAsString());
        break;
    }
  }

  private void start(final WebSocketSession session, JsonObject jsonMessage) {
    ...
  }

  private void sendError(WebSocketSession session, String message) {
    ...
  }
}

Following snippet shows method start, where ICE candidates are gathered and Media Pipeline and Media Elements (WebRtcEndpoint and KmsSendData) are created and connected. Message startResponse is sent back to client carrying the SDP answer.

private void start(final WebSocketSession session, JsonObject jsonMessage) {
   try {
      // User session
      UserSession user = new UserSession();
      MediaPipeline pipeline = kurento.createMediaPipeline();
      user.setMediaPipeline(pipeline);
      WebRtcEndpoint webRtcEndpoint = new WebRtcEndpoint.Builder(pipeline).useDataChannels()
          .build();
      user.setWebRtcEndpoint(webRtcEndpoint);
      users.put(session.getId(), user);

      // ICE candidates
      webRtcEndpoint.addIceCandidateFoundListener(new EventListener<IceCandidateFoundEvent>() {
        @Override
        public void onEvent(IceCandidateFoundEvent event) {
          JsonObject response = new JsonObject();
          response.addProperty("id", "iceCandidate");
          response.add("candidate", JsonUtils.toJsonObject(event.getCandidate()));
          try {
            synchronized (session) {
              session.sendMessage(new TextMessage(response.toString()));
            }
          } catch (IOException e) {
            log.debug(e.getMessage());
          }
        }
      });

      // Media logic
      KmsShowData kmsShowData = new KmsShowData.Builder(pipeline).build();

      webRtcEndpoint.connect(kmsShowData);
      kmsShowData.connect(webRtcEndpoint);

      // SDP negotiation (offer and answer)
      String sdpOffer = jsonMessage.get("sdpOffer").getAsString();
      String sdpAnswer = webRtcEndpoint.processOffer(sdpOffer);

      JsonObject response = new JsonObject();
      response.addProperty("id", "startResponse");
      response.addProperty("sdpAnswer", sdpAnswer);

      synchronized (session) {
        session.sendMessage(new TextMessage(response.toString()));
      }

      webRtcEndpoint.gatherCandidates();

    } catch (Throwable t) {
      sendError(session, t.getMessage());
    }
 }

The sendError method is quite simple: it sends an error message to the client when an exception is caught in the server-side.

private void sendError(WebSocketSession session, String message) {
   try {
      JsonObject response = new JsonObject();
      response.addProperty("id", "error");
      response.addProperty("message", message);
      session.sendMessage(new TextMessage(response.toString()));
   } catch (IOException e) {
      log.error("Exception sending message", e);
   }
}
Client-Side Logic

Let’s move now to the client-side of the application. To call the previously created WebSocket service in the server-side, we use the JavaScript class WebSocket. We use a specific Kurento JavaScript library called kurento-utils.js to simplify the WebRTC interaction with the server. This library depends on adapter.js, which is a JavaScript WebRTC utility maintained by Google that abstracts away browser differences. Finally jquery.js is also needed in this application.

These libraries are linked in the index.html web page, and are used in the index.js. In the following snippet we can see the creation of the WebSocket (variable ws) in the path /showdatachannel. Then, the onmessage listener of the WebSocket is used to implement the JSON signaling protocol in the client-side. Notice that there are three incoming messages to client: startResponse, error, and iceCandidate. Convenient actions are taken to implement each step in the communication. For example, in functions start the function WebRtcPeer.WebRtcPeerSendrecv of kurento-utils.js is used to start a WebRTC communication.

var ws = new WebSocket('wss://' + location.host + '/showdatachannel');

ws.onmessage = function(message) {
   var parsedMessage = JSON.parse(message.data);
   console.info('Received message: ' + message.data);

   switch (parsedMessage.id) {
   case 'startResponse':
      startResponse(parsedMessage);
      break;
   case 'error':
      if (state == I_AM_STARTING) {
         setState(I_CAN_START);
      }
      onError("Error message from server: " + parsedMessage.message);
      break;
   case 'iceCandidate':
      webRtcPeer.addIceCandidate(parsedMessage.candidate, function(error) {
         if (error) {
            console.error("Error adding candidate: " + error);
            return;
         }
      });
      break;
   default:
      if (state == I_AM_STARTING) {
         setState(I_CAN_START);
      }
      onError('Unrecognized message', parsedMessage);
   }
}

function start() {
   console.log("Starting video call ...")
   // Disable start button
   setState(I_AM_STARTING);
   showSpinner(videoInput, videoOutput);

   var servers = null;
    var configuration = null;
    var peerConnection = new RTCPeerConnection(servers, configuration);

    console.log("Creating channel");
    var dataConstraints = null;

    channel = peerConnection.createDataChannel(getChannelName (), dataConstraints);

    channel.onopen = onSendChannelStateChange;
    channel.onclose = onSendChannelStateChange;

    function onSendChannelStateChange(){
        if(!channel) return;
        var readyState = channel.readyState;
        console.log("sencChannel state changed to " + readyState);
        if(readyState == 'open'){
          dataChannelSend.disabled = false;
          dataChannelSend.focus();
          $('#send').attr('disabled', false);
        } else {
          dataChannelSend.disabled = true;
          $('#send').attr('disabled', true);
        }
      }

    var sendButton = document.getElementById('send');
    var dataChannelSend = document.getElementById('dataChannelSend');

    sendButton.addEventListener("click", function(){
        var data = dataChannelSend.value;
        console.log("Send button pressed. Sending data " + data);
        channel.send(data);
        dataChannelSend.value = "";
      });

   console.log("Creating WebRtcPeer and generating local sdp offer ...");

   var options = {
      peerConnection: peerConnection,
      localVideo : videoInput,
      remoteVideo : videoOutput,
      onicecandidate : onIceCandidate
   }
   webRtcPeer = new kurentoUtils.WebRtcPeer.WebRtcPeerSendrecv(options,
         function(error) {
            if (error) {
               return console.error(error);
            }
            webRtcPeer.generateOffer(onOffer);
         });
}

function closeChannels(){

   if(channel){
     channel.close();
     $('#dataChannelSend').disabled = true;
     $('#send').attr('disabled', true);
     channel = null;
   }
}

function onOffer(error, offerSdp) {
   if (error)
      return console.error("Error generating the offer");
   console.info('Invoking SDP offer callback function ' + location.host);
   var message = {
      id : 'start',
      sdpOffer : offerSdp
   }
   sendMessage(message);
}

function onError(error) {
   console.error(error);
}

function onIceCandidate(candidate) {
   console.log("Local candidate" + JSON.stringify(candidate));

   var message = {
      id : 'onIceCandidate',
      candidate : candidate
   };
   sendMessage(message);
}

function startResponse(message) {
   setState(I_CAN_STOP);
   console.log("SDP answer received from server. Processing ...");

   webRtcPeer.processAnswer(message.sdpAnswer, function(error) {
      if (error)
         return console.error(error);
   });
}

function stop() {
   console.log("Stopping video call ...");
   setState(I_CAN_START);
   if (webRtcPeer) {
       closeChannels();

      webRtcPeer.dispose();
      webRtcPeer = null;

      var message = {
         id : 'stop'
      }
      sendMessage(message);
   }
   hideSpinner(videoInput, videoOutput);
}

function sendMessage(message) {
   var jsonMessage = JSON.stringify(message);
   console.log('Senging message: ' + jsonMessage);
   ws.send(jsonMessage);
}
Dependencies

This Java Spring application is implemented using Maven. The relevant part of the pom.xml is where Kurento dependencies are declared. As the following snippet shows, we need two dependencies: the Kurento Client Java dependency (kurento-client) and the JavaScript Kurento utility library (kurento-utils) for the client-side. Other client libraries are managed with webjars:

<dependencies>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-client</artifactId>
   </dependency>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-utils-js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars</groupId>
      <artifactId>webjars-locator</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>bootstrap</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>demo-console</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>adapter.js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>jquery</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>ekko-lightbox</artifactId>
   </dependency>
</dependencies>

注解

We are in active development. You can find the latest version of Kurento Java Client at Maven Central.

Kurento Java Client has a minimum requirement of Java 7. Hence, you need to include the following properties in your pom:

<maven.compiler.target>1.7</maven.compiler.target>
<maven.compiler.source>1.7</maven.compiler.source>

JavaScript - Hello World with Data Channels

This web application extends the Hello World Tutorial, adding media processing to the basic WebRTC loopback and allowing send text from browser to the media server through data channels.

For the impatient: running this example

You’ll need to install Kurento Media Server before running this example. Read installation guide for further information.

Be sure to have installed Node.js and Bower in your system. In an Ubuntu machine, you can install both as follows:

curl -sL https://deb.nodesource.com/setup_4.x | sudo bash -
sudo apt-get install -y nodejs
sudo npm install -g bower

Due to Same-origin policy, this demo has to be served by an HTTP server. A very simple way of doing this is by means of an HTTP Node.js server which can be installed using npm :

sudo npm install http-server -g

You also need the source code of this demo. You can clone it from GitHub. Then start the HTTP server:

git clone https://github.com/Kurento/kurento-tutorial-js.git
cd kurento-tutorial-js/kurento-hello-world-data-channel
git checkout 6.6.1
bower install
http-server -p 8443 -S -C keys/server.crt -K keys/server.key

Finally, access the application connecting to the URL https://localhost:8443/ through a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the parameter ws_uri to the URL, as follows:

https://localhost:8443/index.html?ws_uri=wss://kms_host:kms_port/kurento

Notice that the Kurento Media Server must connected using a Secure WebSocket (i.e., the KMS URI starts with wss://). For this reason, the support for secure WebSocket must be enabled in the Kurento Media Server you are using to run this tutorial. For further information about securing applications, please visit the following page.

注解

This demo needs the kms-datachannelexample module installed in the media server. That module is available in the Kurento repositories, so it is possible to install it with:

sudo apt-get install kms-datachannelexample
Understanding this example

The logic of the application is quite simple: the local stream is sent to Kurento Media Server, which returns it back to the client without modifications. To implement this behavior we need to create a Media Pipeline with a single Media Element, i.e. of type WebRtcEndpoint, which holds the capability of exchanging full-duplex (bidirectional) WebRTC media flows. It is important to set value of property useDataChannels to true during WebRtcEndpoint creation. This media element is connected to itself in order to deliver back received Media.

The application creates a channel between PeerConnection and WebRtcEndpoint used for message delivery.

Complete source code of this demo can be found in GitHub.

JavaScript Logic

This demo follows a Single Page Application architecture (SPA). The interface is the following HTML page: index.html. This web page links two Kurento JavaScript libraries:

  • kurento-client.js : Implementation of the Kurento JavaScript Client.
  • kurento-utils.js : Kurento utility library aimed to simplify the WebRTC management in the browser.

In addition, these two JavaScript libraries are also required:

  • Bootstrap : Web framework for developing responsive web sites.
  • jquery.js : Cross-platform JavaScript library designed to simplify the client-side scripting of HTML.
  • adapter.js : WebRTC JavaScript utility library maintained by Google that abstracts away browser differences.
  • ekko-lightbox : Module for Bootstrap to open modal images, videos, and galleries.
  • demo-console : Custom JavaScript console.

The specific logic of this demo is coded in the following JavaScript page: index.js. In this file, there is a function which is called when the green button labeled as Start in the GUI is clicked.

var startButton = document.getElementById("start");

startButton.addEventListener("click", function() {
   var options = {
      peerConnection: peerConnection,
      localVideo: videoInput,
      remoteVideo: videoOutput
    };

   webRtcPeer = kurentoUtils.WebRtcPeer.WebRtcPeerSendrecv(options, function(error) {
      if(error) return onError(error)
      this.generateOffer(onOffer)
   });

   [...]
}

The function WebRtcPeer.WebRtcPeerSendrecv abstracts the WebRTC internal details (i.e. PeerConnection and getUserStream) and makes possible to start a full-duplex WebRTC communication, using the HTML video tag with id videoInput to show the video camera (local stream) and the video tag videoOutput to show the remote stream provided by the Kurento Media Server.

Inside this function, a call to generateOffer is performed. This function accepts a callback in which the SDP offer is received. In this callback we create an instance of the KurentoClient class that will manage communications with the Kurento Media Server. So, we need to provide the URI of its WebSocket endpoint. In this example, we assume it’s listening in port 8433 at the same host than the HTTP serving the application.

[...]

var args = getopts(location.search,
{
  default:
  {
    ws_uri: 'wss://' + location.hostname + ':8433/kurento',
    ice_servers: undefined
  }
});

[...]

kurentoClient(args.ws_uri, function(error, client){
  [...]
};

Once we have an instance of kurentoClient, the following step is to create a Media Pipeline, as follows:

client.create("MediaPipeline", function(error, _pipeline){
   [...]
});

If everything works correctly, we have an instance of a media pipeline (variable pipeline in this example). With this instance, we are able to create Media Elements. In this example we just need a WebRtcEndpoint with useDataChannels property as true. Then, this media elements is connected itself:

pipeline.create("WebRtcEndpoint", {useDataChannels: true}, function(error, webRtc){
   if(error) return onError(error);

   setIceCandidateCallbacks(webRtcPeer, webRtc, onError)

   webRtc.processOffer(sdpOffer, function(error, sdpAnswer){
     if(error) return onError(error);

     webRtc.gatherCandidates(onError);

     webRtcPeer.processAnswer(sdpAnswer, onError);
   });

   webRtc.connect(webRtc, function(error){
     if(error) return onError(error);

     console.log("Loopback established");
   });
 });

In the following snippet, we can see how to create the channel and the send method of one channel.

var dataConstraints = null;
var channel = peerConnection.createDataChannel(getChannelName (), dataConstraints);
...

sendButton.addEventListener("click", function(){
    ...
    channel.send(data);
    ...
});

注解

The TURN and STUN servers to be used can be configured simple adding the parameter ice_servers to the application URL, as follows:

https://localhost:8443/index.html?ice_servers=[{"urls":"stun:stun1.example.net"},{"urls":"stun:stun2.example.net"}]
https://localhost:8443/index.html?ice_servers=[{"urls":"turn:turn.example.org","username":"user","credential":"myPassword"}]
Dependencies

Demo dependencies are defined in file bower.json. They are managed using Bower.

"dependencies": {
   "kurento-client": "6.6.0",
   "kurento-utils": "6.6.2"
}

注解

We are in active development. You can find the latest version of Kurento JavaScript Client at Bower.

WebRTC recording

This tutorial has two parts. First, it implements a WebRTC loopback and records the stream to disk. Second, it plays back the recorded stream. Users can choose which type of media to send and record: audio, video or both.

Java - Recorder

This web application extends Hello World adding recording capabilities.

注解

This tutorial has been configured to use https. Follow the instructions to secure your application.

For the impatient: running this example

You need to have installed the Kurento Media Server before running this example. Read the installation guide for further information.

To launch the application, you need to clone the GitHub project where this demo is hosted, and then run the main class:

git clone https://github.com/Kurento/kurento-tutorial-java.git
cd kurento-tutorial-java/kurento-hello-world-recording
git checkout 6.6.2
mvn compile exec:java

Access the application connecting to the URL https://localhost:8443/ in a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the flag kms.url to the JVM executing the demo. As we’ll be using maven, you should execute the following command

mvn compile exec:java -Dkms.url=ws://kms_host:kms_port/kurento
Understanding this example

In the first part of this tutorial, the local stream is sent to the media server, which in turn sends it back to the client, while recording it at the same time. In order to implement this behavior, we need to create a Media Pipeline consisting on a WebRtcEndpoint and a RecorderEnpoint.

The second part of this demo shows how to play recorded media. To achieve this, we need to create a Media Pipeline composed by a WebRtcEndpoint and a PlayerEndpoint. The uri property of the player is the uri of the recorded file.

This is a web application, and therefore it follows a client-server architecture. At the client-side, the logic is implemented in JavaScript. At the server-side, we use a Spring-Boot based server application consuming the Kurento Java Client API, to control Kurento Media Server capabilities. All in all, the high level architecture of this demo is three-tier. To communicate these entities, two WebSockets are used. First, a WebSocket is created between client and application server to implement a custom signaling protocol. Second, another WebSocket is used to perform the communication between the Kurento Java Client and the Kurento Media Server. This communication takes place using the Kurento Protocol. For further information on it, please see this page of the documentation.

The following sections analyze in depth the server (Java) and client-side (JavaScript) code of this application. The complete source code can be found in GitHub.

Application Server Logic

This demo has been developed using Java in the server-side, based on the Spring Boot framework, which embeds a Tomcat web server within the generated maven artifact, and thus simplifies the development and deployment process.

注解

You can use whatever Java server side technology you prefer to build web applications with Kurento. For example, a pure Java EE application, SIP Servlets, Play, Vert.x, etc. Here we chose Spring Boot for convenience.

The main class of this demo is HelloWorldRecApp. As you can see, the KurentoClient is instantiated in this class as a Spring Bean. This bean is used to create Kurento Media Pipelines, which are used to add media capabilities to the application. In this instantiation we see that we need to specify to the client library the location of the Kurento Media Server. In this example, we assume it is located at localhost listening in port 8888. If you reproduce this example you’ll need to insert the specific location of your Kurento Media Server instance there.

Once the Kurento Client has been instantiated, you are ready for communicating with Kurento Media Server and controlling its multimedia capabilities.

@SpringBootApplication
@EnableWebSocket
public class HelloWorldRecApp implements WebSocketConfigurer {

  @Bean
  public HelloWorldRecHandler handler() {
    return new HelloWorldRecHandler();
  }

  @Bean
  public KurentoClient kurentoClient() {
    return KurentoClient.create();
  }

  @Override
  public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
    registry.addHandler(handler(), "/recording");
  }

  @Bean
  public UserRegistry registry() {
    return new UserRegistry();
  }

  public static void main(String[] args) throws Exception {
    new SpringApplication(HelloWorldRecApp.class).run(args);
  }
}

This web application follows a Single Page Application architecture (SPA), and uses a WebSocket to communicate client with application server by means of requests and responses. Specifically, the main app class implements the interface WebSocketConfigurer to register a WebSocketHanlder to process WebSocket requests in the path /recording.

HelloWorldRecHandler class implements TextWebSocketHandler to handle text WebSocket requests. The central piece of this class is the method handleTextMessage. This method implements the actions for requests, returning responses through the WebSocket. In other words, it implements the server part of the signaling protocol depicted in the previous sequence diagram.

In the designed protocol there are three different kinds of incoming messages to the Server : start, stop , play and onIceCandidates. These messages are treated in the switch clause, taking the proper steps in each case.

public class HelloWorldRecHandler extends TextWebSocketHandler {

  private static final String RECORDER_FILE_PATH = "file:///tmp/HelloWorldRecorded.webm";

  private final Logger log = LoggerFactory.getLogger(HelloWorldRecHandler.class);
  private static final Gson gson = new GsonBuilder().create();

  @Autowired
  private UserRegistry registry;

  @Autowired
  private KurentoClient kurento;

  @Override
  public void handleTextMessage(WebSocketSession session, TextMessage message) throws Exception {
    JsonObject jsonMessage = gson.fromJson(message.getPayload(), JsonObject.class);

    log.debug("Incoming message: {}", jsonMessage);

    UserSession user = registry.getBySession(session);
    if (user != null) {
      log.debug("Incoming message from user '{}': {}", user.getId(), jsonMessage);
    } else {
      log.debug("Incoming message from new user: {}", jsonMessage);
    }

    switch (jsonMessage.get("id").getAsString()) {
      case "start":
        start(session, jsonMessage);
        break;
      case "stop":
      case "stopPlay":
        if (user != null) {
          user.release();
        }
        break;
      case "play":
        play(user, session, jsonMessage);
        break;
      case "onIceCandidate": {
        JsonObject jsonCandidate = jsonMessage.get("candidate").getAsJsonObject();

        if (user != null) {
          IceCandidate candidate = new IceCandidate(jsonCandidate.get("candidate").getAsString(),
              jsonCandidate.get("sdpMid").getAsString(),
              jsonCandidate.get("sdpMLineIndex").getAsInt());
          user.addCandidate(candidate);
        }
        break;
      }
      default:
        sendError(session, "Invalid message with id " + jsonMessage.get("id").getAsString());
        break;
    }
  }

  private void start(final WebSocketSession session, JsonObject jsonMessage) {
   ...
  }


  private void play(UserSession user, final WebSocketSession session, JsonObject jsonMessage) {
   ...
  }

  private void sendError(WebSocketSession session, String message) {
   ...
  }
}

In the following snippet, we can see the start method. It handles the ICE candidates gathering, creates a Media Pipeline, creates the Media Elements (WebRtcEndpoint and RecorderEndpoint) and make the connections among them. A startResponse message is sent back to the client with the SDP answer.

private void start(final WebSocketSession session, JsonObject jsonMessage) {
    try {

      // 1. Media logic (webRtcEndpoint in loopback)
      MediaPipeline pipeline = kurento.createMediaPipeline();
      WebRtcEndpoint webRtcEndpoint = new WebRtcEndpoint.Builder(pipeline).build();
      webRtcEndpoint.connect(webRtcEndpoint);

      MediaProfileSpecType profile = getMediaProfileFromMessage(jsonMessage);

      RecorderEndpoint recorder = new RecorderEndpoint.Builder(pipeline, RECORDER_FILE_PATH)
          .withMediaProfile(profile).build();

      connectAccordingToProfile(webRtcEndpoint, recorder, profile);

      // 2. Store user session
      UserSession user = new UserSession(session);
      user.setMediaPipeline(pipeline);
      user.setWebRtcEndpoint(webRtcEndpoint);
      registry.register(user);

      // 3. SDP negotiation
      String sdpOffer = jsonMessage.get("sdpOffer").getAsString();
      String sdpAnswer = webRtcEndpoint.processOffer(sdpOffer);

      // 4. Gather ICE candidates
      webRtcEndpoint.addIceCandidateFoundListener(new EventListener<IceCandidateFoundEvent>() {
        @Override
        public void onEvent(IceCandidateFoundEvent event) {
          JsonObject response = new JsonObject();
          response.addProperty("id", "iceCandidate");
          response.add("candidate", JsonUtils.toJsonObject(event.getCandidate()));
          try {
            synchronized (session) {
              session.sendMessage(new TextMessage(response.toString()));
            }
          } catch (IOException e) {
            log.error(e.getMessage());
          }
        }
      });

      JsonObject response = new JsonObject();
      response.addProperty("id", "startResponse");
      response.addProperty("sdpAnswer", sdpAnswer);

      synchronized (user) {
        session.sendMessage(new TextMessage(response.toString()));
      }

      webRtcEndpoint.gatherCandidates();

      recorder.record();
    } catch (Throwable t) {
      log.error("Start error", t);
      sendError(session, t.getMessage());
    }
  }

The play method, creates a Media Pipeline with the Media Elements (WebRtcEndpoint and PlayerEndpoint) and make the connections among them. It will then send the recorded media to the client.

private void play(UserSession user, final WebSocketSession session, JsonObject jsonMessage) {
    try {

      // 1. Media logic
      final MediaPipeline pipeline = kurento.createMediaPipeline();
      WebRtcEndpoint webRtcEndpoint = new WebRtcEndpoint.Builder(pipeline).build();
      PlayerEndpoint player = new PlayerEndpoint.Builder(pipeline, RECORDER_FILE_PATH).build();
      player.connect(webRtcEndpoint);

      // Player listeners
      player.addErrorListener(new EventListener<ErrorEvent>() {
        @Override
        public void onEvent(ErrorEvent event) {
          log.info("ErrorEvent for session '{}': {}", session.getId(), event.getDescription());
          sendPlayEnd(session, pipeline);
        }
      });
      player.addEndOfStreamListener(new EventListener<EndOfStreamEvent>() {
        @Override
        public void onEvent(EndOfStreamEvent event) {
          log.info("EndOfStreamEvent for session '{}'", session.getId());
          sendPlayEnd(session, pipeline);
        }
      });

      // 2. Store user session
      user.setMediaPipeline(pipeline);
      user.setWebRtcEndpoint(webRtcEndpoint);

      // 3. SDP negotiation
      String sdpOffer = jsonMessage.get("sdpOffer").getAsString();
      String sdpAnswer = webRtcEndpoint.processOffer(sdpOffer);

      JsonObject response = new JsonObject();
      response.addProperty("id", "playResponse");
      response.addProperty("sdpAnswer", sdpAnswer);

      // 4. Gather ICE candidates
      webRtcEndpoint.addIceCandidateFoundListener(new EventListener<IceCandidateFoundEvent>() {
        @Override
        public void onEvent(IceCandidateFoundEvent event) {
          JsonObject response = new JsonObject();
          response.addProperty("id", "iceCandidate");
          response.add("candidate", JsonUtils.toJsonObject(event.getCandidate()));
          try {
            synchronized (session) {
              session.sendMessage(new TextMessage(response.toString()));
            }
          } catch (IOException e) {
            log.error(e.getMessage());
          }
        }
      });

      // 5. Play recorded stream
      player.play();

      synchronized (session) {
        session.sendMessage(new TextMessage(response.toString()));
      }

      webRtcEndpoint.gatherCandidates();
    } catch (Throwable t) {
      log.error("Play error", t);
      sendError(session, t.getMessage());
    }
  }

The sendError method is quite simple: it sends an error message to the client when an exception is caught in the server-side.

private void sendError(WebSocketSession session, String message) {
   try {
      JsonObject response = new JsonObject();
      response.addProperty("id", "error");
      response.addProperty("message", message);
      session.sendMessage(new TextMessage(response.toString()));
   } catch (IOException e) {
      log.error("Exception sending message", e);
   }
}
Client-Side Logic

Let’s move now to the client-side of the application. To call the previously created WebSocket service in the server-side, we use the JavaScript class WebSocket. We use a specific Kurento JavaScript library called kurento-utils.js to simplify the WebRTC interaction with the server. This library depends on adapter.js, which is a JavaScript WebRTC utility maintained by Google that abstracts away browser differences. Finally jquery.js is also needed in this application.

These libraries are linked in the index.html web page, and are used in the index.js. In the following snippet we can see the creation of the WebSocket (variable ws) in the path /recording. Then, the onmessage listener of the WebSocket is used to implement the JSON signaling protocol in the client-side. Notice that there are three incoming messages to client: startResponse, playResponse, playEnd,``error``, and iceCandidate. Convenient actions are taken to implement each step in the communication. For example, in functions start the function WebRtcPeer.WebRtcPeerSendrecv of kurento-utils.js is used to start a WebRTC communication.

var ws = new WebSocket('wss://' + location.host + '/recording');

ws.onmessage = function(message) {
   var parsedMessage = JSON.parse(message.data);
   console.info('Received message: ' + message.data);

   switch (parsedMessage.id) {
   case 'startResponse':
      startResponse(parsedMessage);
      break;
   case 'playResponse':
      playResponse(parsedMessage);
      break;
   case 'playEnd':
      playEnd();
      break;
   case 'error':
      setState(NO_CALL);
      onError('Error message from server: ' + parsedMessage.message);
      break;
   case 'iceCandidate':
      webRtcPeer.addIceCandidate(parsedMessage.candidate, function(error) {
         if (error)
            return console.error('Error adding candidate: ' + error);
      });
      break;
   default:
      setState(NO_CALL);
   onError('Unrecognized message', parsedMessage);
   }
}

function start() {
   console.log('Starting video call ...');

   // Disable start button
   setState(DISABLED);
   showSpinner(videoInput, videoOutput);
   console.log('Creating WebRtcPeer and generating local sdp offer ...');

   var options = {
         localVideo : videoInput,
         remoteVideo : videoOutput,
         mediaConstraints : getConstraints(),
         onicecandidate : onIceCandidate
   }

   webRtcPeer = new kurentoUtils.WebRtcPeer.WebRtcPeerSendrecv(options,
         function(error) {
      if (error)
         return console.error(error);
      webRtcPeer.generateOffer(onOffer);
   });
}

function onOffer(error, offerSdp) {
   if (error)
      return console.error('Error generating the offer');
   console.info('Invoking SDP offer callback function ' + location.host);
   var message = {
         id : 'start',
         sdpOffer : offerSdp,
         mode :  $('input[name="mode"]:checked').val()
   }
   sendMessage(message);
}

function onError(error) {
   console.error(error);
}

function onIceCandidate(candidate) {
   console.log('Local candidate' + JSON.stringify(candidate));

   var message = {
         id : 'onIceCandidate',
         candidate : candidate
   };
   sendMessage(message);
}

function startResponse(message) {
   setState(IN_CALL);
   console.log('SDP answer received from server. Processing ...');

   webRtcPeer.processAnswer(message.sdpAnswer, function(error) {
      if (error)
         return console.error(error);
   });
}

function stop() {
   var stopMessageId = (state == IN_CALL) ? 'stop' : 'stopPlay';
   console.log('Stopping video while in ' + state + '...');
   setState(POST_CALL);
   if (webRtcPeer) {
      webRtcPeer.dispose();
      webRtcPeer = null;

      var message = {
            id : stopMessageId
      }
      sendMessage(message);
   }
   hideSpinner(videoInput, videoOutput);
}

function play() {
   console.log("Starting to play recorded video...");

   // Disable start button
   setState(DISABLED);
   showSpinner(videoOutput);

   console.log('Creating WebRtcPeer and generating local sdp offer ...');

   var options = {
         remoteVideo : videoOutput,
         mediaConstraints : getConstraints(),
         onicecandidate : onIceCandidate
   }

   webRtcPeer = new kurentoUtils.WebRtcPeer.WebRtcPeerRecvonly(options,
         function(error) {
      if (error)
         return console.error(error);
      webRtcPeer.generateOffer(onPlayOffer);
   });
}

function onPlayOffer(error, offerSdp) {
   if (error)
      return console.error('Error generating the offer');
   console.info('Invoking SDP offer callback function ' + location.host);
   var message = {
         id : 'play',
         sdpOffer : offerSdp
   }
   sendMessage(message);
}

function getConstraints() {
   var mode = $('input[name="mode"]:checked').val();
   var constraints = {
         audio : true,
         video : true
   }

   if (mode == 'video-only') {
      constraints.audio = false;
   } else if (mode == 'audio-only') {
      constraints.video = false;
   }

   return constraints;
}


function playResponse(message) {
   setState(IN_PLAY);
   webRtcPeer.processAnswer(message.sdpAnswer, function(error) {
      if (error)
         return console.error(error);
   });
}

function playEnd() {
   setState(POST_CALL);
   hideSpinner(videoInput, videoOutput);
}

function sendMessage(message) {
   var jsonMessage = JSON.stringify(message);
   console.log('Senging message: ' + jsonMessage);
   ws.send(jsonMessage);
}
Dependencies

This Java Spring application is implemented using Maven. The relevant part of the pom.xml is where Kurento dependencies are declared. As the following snippet shows, we need two dependencies: the Kurento Client Java dependency (kurento-client) and the JavaScript Kurento utility library (kurento-utils) for the client-side. Other client libraries are managed with webjars:

<dependencies>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-client</artifactId>
   </dependency>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-utils-js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars</groupId>
      <artifactId>webjars-locator</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>bootstrap</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>demo-console</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>adapter.js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>jquery</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>ekko-lightbox</artifactId>
   </dependency>
</dependencies>

注解

We are in active development. You can find the latest version of Kurento Java Client at Maven Central.

Kurento Java Client has a minimum requirement of Java 7. Hence, you need to include the following properties in your pom:

<maven.compiler.target>1.7</maven.compiler.target>
<maven.compiler.source>1.7</maven.compiler.source>

JavaScript - Recorder

This web application extends the Hello World Tutorial, adding recording capabilities.

For the impatient: running this example

You’ll need to install Kurento Media Server before running this example. Read installation guide for further information.

Be sure to have installed Node.js and Bower in your system. In an Ubuntu machine, you can install both as follows:

curl -sL https://deb.nodesource.com/setup_4.x | sudo bash -
sudo apt-get install -y nodejs
sudo npm install -g bower

Due to Same-origin policy, this demo has to be served by an HTTP server. A very simple way of doing this is by means of an HTTP Node.js server which can be installed using npm :

sudo npm install http-server -g

You will need to download the source code form GitHub. There are two implementations of this tutorial, but they are functionally the same. It’s just the internal implementation that changes. After checking out the code, you can start the web server.

git clone https://github.com/Kurento/kurento-tutorial-js.git
cd kurento-tutorial-js/kurento-recorder
git checkout 6.6.1
bower install
http-server -p 8443 -S -C keys/server.crt -K keys/server.key

git clone https://github.com/Kurento/kurento-tutorial-js.git
cd kurento-tutorial-js/kurento-hello-world-recorder-generator
git checkout 6.6.1
bower install
http-server -p 8443 -S -C keys/server.crt -K keys/server.key

Finally, access the application connecting to the URL https://localhost:8443/ through a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the parameter ws_uri to the URL, as follows:

https://localhost:8443/index.html?ws_uri=wss://kms_host:kms_port/kurento

Notice that the Kurento Media Server must connected using a Secure WebSocket (i.e., the KMS URI starts with wss://). For this reason, the support for secure WebSocket must be enabled in the Kurento Media Server you are using to run this tutorial. For further information about securing applications, please visit the following page.

Understanding this example

In the first part of this demo, the local stream is sent to Kurento Media Server, which returns it back to the client and records to the same time. In order to implement this behavior we need to create a`Media Pipeline`:term: consisting of a WebRtcEndpoint and a RecorderEnpoint.

The second part of this demo shows how to play recorded media. To achieve this, we need to create a Media Pipeline composed by a WebRtcEndpoint and a PlayerEndpoint. The uri property of the player is the uri of the recorded file.

There are two implementations for this demo to be found in github:

注解

The snippets are based in demo with callbacks.

JavaScript Logic

This demo follows a Single Page Application architecture (SPA). The interface is the following HTML page: index.html. This web page links two Kurento JavaScript libraries:

  • kurento-client.js : Implementation of the Kurento JavaScript Client.
  • kurento-utils.js : Kurento utility library aimed to simplify the WebRTC management in the browser.

In addition, these two JavaScript libraries are also required:

  • Bootstrap : Web framework for developing responsive web sites.
  • jquery.js : Cross-platform JavaScript library designed to simplify the client-side scripting of HTML.
  • adapter.js : WebRTC JavaScript utility library maintained by Google that abstracts away browser differences.
  • ekko-lightbox : Module for Bootstrap to open modal images, videos, and galleries.
  • demo-console : Custom JavaScript console.

The specific logic of this demo is coded in the following JavaScript page: index.js. In this file, there is a function which is called when the green button, labeled as Start in the GUI, is clicked.

var startRecordButton = document.getElementById("start");

startRecordButton.addEventListener("click", startRecording);

function startRecording() {
   var options = {
     localVideo: videoInput,
     remoteVideo: videoOutput
   };

   webRtcPeer = kurentoUtils.WebRtcPeer.WebRtcPeerSendrecv(options, function(error) {
      if(error) return onError(error)
      this.generateOffer(onOffer)
   });

   [...]
}

The function WebRtcPeer.WebRtcPeerSendrecv abstracts the WebRTC internal details (i.e. PeerConnection and getUserStream) and makes possible to start a full-duplex WebRTC communication, using the HTML video tag with id videoInput to show the video camera (local stream) and the video tag videoOutput to show the remote stream provided by the Kurento Media Server.

Inside this function, a call to generateOffer is performed. This function accepts a callback in which the SDP offer is received. In this callback we create an instance of the KurentoClient class that will manage communications with the Kurento Media Server. So, we need to provide the URI of its WebSocket endpoint. In this example, we assume it’s listening in port 8433 at the same host than the HTTP serving the application.

[...]

var args = getopts(location.search,
{
  default:
  {
    ws_uri: 'wss://' + location.hostname + ':8433/kurento',
    file_uri: 'file:///tmp/recorder_demo.webm', // file to be stored in media server
    ice_servers: undefined
  }
});

[...]

kurentoClient(args.ws_uri, function(error, client){
  [...]
};

Once we have an instance of kurentoClient, the following step is to create a Media Pipeline, as follows:

client.create("MediaPipeline", function(error, _pipeline){
   [...]
});

If everything works correctly, we have an instance of a media pipeline (variable pipeline in this example). With this instance, we are able to create Media Elements. In this example we just need a WebRtcEndpoint and a RecorderEndpoint. Then, these media elements are interconnected:

var elements =
   [
     {type: 'RecorderEndpoint', params: {uri : args.file_uri}},
     {type: 'WebRtcEndpoint', params: {}}
   ]

pipeline.create(elements, function(error, elements){
  if (error) return onError(error);

  var recorder = elements[0]
  var webRtc   = elements[1]

  setIceCandidateCallbacks(webRtcPeer, webRtc, onError)

  webRtc.processOffer(offer, function(error, answer) {
    if (error) return onError(error);

    console.log("offer");

    webRtc.gatherCandidates(onError);
    webRtcPeer.processAnswer(answer);
  });

  client.connect(webRtc, webRtc, recorder, function(error) {
    if (error) return onError(error);

    console.log("Connected");

    recorder.record(function(error) {
      if (error) return onError(error);

      console.log("record");
    });
  });
});

When stop button is clicked, the recoder element stops to record, and all elements are released.

stopRecordButton.addEventListener("click", function(event){
    recorder.stop();
    pipeline.release();
    webRtcPeer.dispose();
    videoInput.src = "";
    videoOutput.src = "";

    hideSpinner(videoInput, videoOutput);

    var playButton = document.getElementById('play');
    playButton.addEventListener('click', startPlaying);
  })

In the second part, after play button is clicked, we have an instance of a media pipeline (variable pipeline in this example). With this instance, we are able to create Media Elements. In this example we just need a WebRtcEndpoint and a PlayerEndpoint with uri option like path where the media was recorded. Then, these media elements are interconnected:

var options = {uri : args.file_uri}

pipeline.create("PlayerEndpoint", options, function(error, player) {
  if (error) return onError(error);

  player.on('EndOfStream', function(event){
    pipeline.release();
    videoPlayer.src = "";

    hideSpinner(videoPlayer);
  });

  player.connect(webRtc, function(error) {
    if (error) return onError(error);

    player.play(function(error) {
      if (error) return onError(error);
      console.log("Playing ...");
    });
  });
});

注解

The TURN and STUN servers to be used can be configured simple adding the parameter ice_servers to the application URL, as follows:

https://localhost:8443/index.html?ice_servers=[{"urls":"stun:stun1.example.net"},{"urls":"stun:stun2.example.net"}]
https://localhost:8443/index.html?ice_servers=[{"urls":"turn:turn.example.org","username":"user","credential":"myPassword"}]
Dependencies

Demo dependencies are located in file bower.json. Bower is used to collect them.

"dependencies": {
   "kurento-client": "6.6.0",
   "kurento-utils": "6.6.2"
}

注解

We are in active development. You can find the latest version of Kurento JavaScript Client at Bower.

WebRTC repository

This is similar to the recording tutorial, but using the repository to store metadata.

Java - Repository

This web application extends Hello World adding recording capabilities by means of the Kurento Repository.

注解

This tutorial has been configured to use https. Follow the instructions to secure your application.

For the impatient: running this example

You need to have installed the Kurento Media Server before running this example. Read the installation guide for further information.

In addition, you also need the kurento-repository-server. This component is in charge of the storage and retrieval of the media. Please visit the Kurento Repository Server installation guide for further details.

To launch the application, you need to clone the GitHub project where this demo is hosted, and then run the main class:

git clone https://github.com/Kurento/kurento-tutorial-java.git
cd kurento-tutorial-java/kurento-hello-world-repository/
git checkout 6.6.2
mvn compile exec:java

Access the application connecting to the URL https://localhost:8443/ in a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the flag kms.url to the JVM executing the demo. In addition, by default this demo is also suppossing that the Kurento Repository is up and running in the localhost. It can be changed by means of the property repository.uri. All in all, and due to the fact that we can use Maven to run the tutorial, you should execute the following command:

mvn compile exec:java -Dkms.url=ws://kms_host:kms_port/kurento \
    -Drepository.uri=http://repository_host:repository_url
Understanding this example

On top of the recording capabilities from the base tutorial, this application creates a repository element to store media in that repository. Additionally, metadata about the recorded file can be also stored in the repository.

This is a web application, and therefore it follows a client-server architecture. At the client-side, the logic is implemented in JavaScript. At the server-side, we use a Spring-Boot based server application consuming the Kurento Java Client API, to control Kurento Media Server capabilities. All in all, the high level architecture of this demo is three-tier. To communicate these entities, two WebSockets are used. First, a WebSocket is created between client and application server to implement a custom signaling protocol. Second, another WebSocket is used to perform the communication between the Kurento Java Client and the Kurento Media Server. This communication takes place using the Kurento Protocol. For further information on it, please see this page of the documentation.

The following sections analyze in deep the server (Java) and client-side (JavaScript) code of this application. The complete source code can be found in GitHub.

Application Server Logic

This demo has been developed using Java in the server-side, based on the Spring Boot framework, which embeds a Tomcat web server within the generated maven artifact, and thus simplifies the development and deployment process.

注解

You can use whatever Java server side technology you prefer to build web applications with Kurento. For example, a pure Java EE application, SIP Servlets, Play, Vert.x, etc. Here we chose Spring Boot for convenience.

The main class of this demo is HelloWorldRecApp. As you can see, the KurentoClient is instantiated in this class as a Spring Bean. This bean is used to create Kurento Media Pipelines, which are used to add media capabilities to the application. In this instantiation we see that we need to specify to the client library the location of the Kurento Media Server. In this example, we assume it is located at localhost listening in port 8888. If you reproduce this example you’ll need to insert the specific location of your Kurento Media Server instance there.

Once the Kurento Client has been instantiated, you are ready for communicating with Kurento Media Server and controlling its multimedia capabilities.

@SpringBootApplication
@EnableWebSocket
public class HelloWorldRecApp implements WebSocketConfigurer {

  protected static final String DEFAULT_REPOSITORY_SERVER_URI = "http://localhost:7676";

  protected static final String REPOSITORY_SERVER_URI =
    System.getProperty("repository.uri", DEFAULT_REPOSITORY_SERVER_URI);

  @Bean
  public HelloWorldRecHandler handler() {
    return new HelloWorldRecHandler();
  }

  @Bean
  public KurentoClient kurentoClient() {
    return KurentoClient.create();
  }

  @Override
  public void registerWebSocketHandlers(WebSocketHandlerRegistry registry) {
    registry.addHandler(handler(), "/repository");
  }

  @Bean
  public RepositoryClient repositoryServiceProvider() {
    return REPOSITORY_SERVER_URI.startsWith("file://") ? null
      : RepositoryClientProvider.create(REPOSITORY_SERVER_URI);
  }

  @Bean
  public UserRegistry registry() {
    return new UserRegistry();
  }

  public static void main(String[] args) throws Exception {
    new SpringApplication(HelloWorldRecApp.class).run(args);
  }
}

This web application follows a Single Page Application architecture (SPA), and uses a WebSocket to communicate client with application server by means of requests and responses. Specifically, the main app class implements the interface WebSocketConfigurer to register a WebSocketHanlder to process WebSocket requests in the path /repository.

HelloWorldRecHandler class implements TextWebSocketHandler to handle text WebSocket requests. The central piece of this class is the method handleTextMessage. This method implements the actions for requests, returning responses through the WebSocket. In other words, it implements the server part of the signaling protocol depicted in the previous sequence diagram.

In the designed protocol there are three different kinds of incoming messages to the Server : start, stop, stopPlay, play and onIceCandidates. These messages are treated in the switch clause, taking the proper steps in each case.

public class HelloWorldRecHandler extends TextWebSocketHandler {

  // slightly larger timeout
  private static final int REPOSITORY_DISCONNECT_TIMEOUT = 5500;

  private static final String RECORDING_EXT = ".webm";

  private final Logger log = LoggerFactory.getLogger(HelloWorldRecHandler.class);
  private static final SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd_HH-mm-ss-S");
  private static final Gson gson = new GsonBuilder().create();

  @Autowired
  private UserRegistry registry;

  @Autowired
  private KurentoClient kurento;

  @Autowired
  private RepositoryClient repositoryClient;

  @Override
  public void handleTextMessage(WebSocketSession session, TextMessage message) throws Exception {
    JsonObject jsonMessage = gson.fromJson(message.getPayload(), JsonObject.class);

    log.debug("Incoming message: {}", jsonMessage);

    UserSession user = registry.getBySession(session);
    if (user != null) {
      log.debug("Incoming message from user '{}': {}", user.getId(), jsonMessage);
    } else {
      log.debug("Incoming message from new user: {}", jsonMessage);
    }

    switch (jsonMessage.get("id").getAsString()) {
      case "start":
        start(session, jsonMessage);
        break;
      case "stop":
      case "stopPlay":
        if (user != null) {
          user.release();
        }
        break;
      case "play":
        play(user, session, jsonMessage);
        break;
      case "onIceCandidate": {
        JsonObject jsonCandidate = jsonMessage.get("candidate").getAsJsonObject();

        if (user != null) {
          IceCandidate candidate = new IceCandidate(jsonCandidate.get("candidate").getAsString(),
              jsonCandidate.get("sdpMid").getAsString(),
              jsonCandidate.get("sdpMLineIndex").getAsInt());
          user.addCandidate(candidate);
        }
        break;
      }
      default:
        sendError(session, "Invalid message with id " + jsonMessage.get("id").getAsString());
        break;
    }
  }

  private void start(final WebSocketSession session, JsonObject jsonMessage) {
   ...
  }

  private void play(UserSession user, final WebSocketSession session, JsonObject jsonMessage) {
    ...
  }

  private void sendError(WebSocketSession session, String message) {
    ...
  }
}

In the following snippet, we can see the start method. If a repository REST client or interface has been created, it will obtain a RepositoryItem from the remote service. This item contains an ID and a recording URI that will be used by the Kurento Media Server. The ID will be used after the recording ends in order to manage the stored media. If the client doesn’t exist, the recording will be performed to a local URI, on the same machine as the KMS. This method also deals with the ICE candidates gathering, creates a Media Pipeline, creates the Media Elements (WebRtcEndpoint and RecorderEndpoint) and makes the connections between them. A startResponse message is sent back to the client with the SDP answer.

private void start(final WebSocketSession session, JsonObject jsonMessage) {
   try {
      // 0. Repository logic
      RepositoryItemRecorder repoItem = null;
      if (repositoryClient != null) {
        try {
          Map<String, String> metadata = Collections.emptyMap();
          repoItem = repositoryClient.createRepositoryItem(metadata);
        } catch (Exception e) {
          log.warn("Unable to create kurento repository items", e);
        }
      } else {
        String now = df.format(new Date());
        String filePath = HelloWorldRecApp.REPOSITORY_SERVER_URI + now + RECORDING_EXT;
        repoItem = new RepositoryItemRecorder();
        repoItem.setId(now);
        repoItem.setUrl(filePath);
      }
      log.info("Media will be recorded {}by KMS: id={} , url={}",
          (repositoryClient == null ? "locally" : ""), repoItem.getId(), repoItem.getUrl());

      // 1. Media logic (webRtcEndpoint in loopback)
      MediaPipeline pipeline = kurento.createMediaPipeline();
      WebRtcEndpoint webRtcEndpoint = new WebRtcEndpoint.Builder(pipeline).build();
      webRtcEndpoint.connect(webRtcEndpoint);
      RecorderEndpoint recorder = new RecorderEndpoint.Builder(pipeline, repoItem.getUrl())
          .withMediaProfile(MediaProfileSpecType.WEBM).build();
      webRtcEndpoint.connect(recorder);

      // 2. Store user session
      UserSession user = new UserSession(session);
      user.setMediaPipeline(pipeline);
      user.setWebRtcEndpoint(webRtcEndpoint);
      user.setRepoItem(repoItem);
      registry.register(user);

      // 3. SDP negotiation
      String sdpOffer = jsonMessage.get("sdpOffer").getAsString();
      String sdpAnswer = webRtcEndpoint.processOffer(sdpOffer);

      // 4. Gather ICE candidates
      webRtcEndpoint.addIceCandidateFoundListener(new EventListener<IceCandidateFoundEvent>() {
        @Override
        public void onEvent(IceCandidateFoundEvent event) {
          JsonObject response = new JsonObject();
          response.addProperty("id", "iceCandidate");
          response.add("candidate", JsonUtils.toJsonObject(event.getCandidate()));
          try {
            synchronized (session) {
              session.sendMessage(new TextMessage(response.toString()));
            }
          } catch (IOException e) {
            log.error(e.getMessage());
          }
        }
  }

The play method, creates a Media Pipeline with the Media Elements (WebRtcEndpoint and PlayerEndpoint) and make the connections between them. It will then send the recorded media to the client. The media can be served from the repository or directly from the disk. If the repository interface exists, it will try to connect to the remote service in order to obtain an URI from which the KMS will read the media streams. The inner workings of the repository restrict reading an item before it has been closed (after the upload finished). This will happen only when a certain number of seconds elapse after the last byte of media is uploaded by the KMS (safe-guard for gaps in the network communications).

private void play(UserSession user, final WebSocketSession session, JsonObject jsonMessage) {
   try {
      // 0. Repository logic
      RepositoryItemPlayer itemPlayer = null;
      if (repositoryClient != null) {
        try {
          Date stopTimestamp = user.getStopTimestamp();
          if (stopTimestamp != null) {
            Date now = new Date();
            long diff = now.getTime() - stopTimestamp.getTime();
            if (diff >= 0 && diff < REPOSITORY_DISCONNECT_TIMEOUT) {
              log.info(
                  "Waiting for {}ms before requesting the repository read endpoint "
                      + "(requires {}ms before upload is considered terminated "
                      + "and only {}ms have passed)",
                  REPOSITORY_DISCONNECT_TIMEOUT - diff, REPOSITORY_DISCONNECT_TIMEOUT, diff);
              Thread.sleep(REPOSITORY_DISCONNECT_TIMEOUT - diff);
            }
          } else {
            log.warn("No stop timeout was found, repository endpoint might not be ready");
          }
          itemPlayer = repositoryClient.getReadEndpoint(user.getRepoItem().getId());
        } catch (Exception e) {
          log.warn("Unable to obtain kurento repository endpoint", e);
        }
      } else {
        itemPlayer = new RepositoryItemPlayer();
        itemPlayer.setId(user.getRepoItem().getId());
        itemPlayer.setUrl(user.getRepoItem().getUrl());
      }
      log.debug("Playing from {}: id={}, url={}",
          (repositoryClient == null ? "disk" : "repository"), itemPlayer.getId(),
          itemPlayer.getUrl());

      // 1. Media logic
      final MediaPipeline pipeline = kurento.createMediaPipeline();
      WebRtcEndpoint webRtcEndpoint = new WebRtcEndpoint.Builder(pipeline).build();
      PlayerEndpoint player = new PlayerEndpoint.Builder(pipeline, itemPlayer.getUrl()).build();
      player.connect(webRtcEndpoint);

      // Player listeners
      player.addErrorListener(new EventListener<ErrorEvent>() {
        @Override
        public void onEvent(ErrorEvent event) {
          log.info("ErrorEvent for session '{}': {}", session.getId(), event.getDescription());
          sendPlayEnd(session, pipeline);
        }
      });
      player.addEndOfStreamListener(new EventListener<EndOfStreamEvent>() {
        @Override
        public void onEvent(EndOfStreamEvent event) {
          log.info("EndOfStreamEvent for session '{}'", session.getId());
          sendPlayEnd(session, pipeline);
        }
      });

      // 2. Store user session
      user.setMediaPipeline(pipeline);
      user.setWebRtcEndpoint(webRtcEndpoint);

      // 3. SDP negotiation
      String sdpOffer = jsonMessage.get("sdpOffer").getAsString();
      String sdpAnswer = webRtcEndpoint.processOffer(sdpOffer);

      JsonObject response = new JsonObject();
      response.addProperty("id", "playResponse");
      response.addProperty("sdpAnswer", sdpAnswer);

      // 4. Gather ICE candidates
      webRtcEndpoint.addIceCandidateFoundListener(new EventListener<IceCandidateFoundEvent>() {
        @Override
        public void onEvent(IceCandidateFoundEvent event) {
          JsonObject response = new JsonObject();
          response.addProperty("id", "iceCandidate");
          response.add("candidate", JsonUtils.toJsonObject(event.getCandidate()));
          try {
            synchronized (session) {
              session.sendMessage(new TextMessage(response.toString()));
            }
          } catch (IOException e) {
            log.error(e.getMessage());
          }
        }
  });

The sendError method is quite simple: it sends an error message to the client when an exception is caught in the server-side.

private void sendError(WebSocketSession session, String message) {
   try {
      JsonObject response = new JsonObject();
      response.addProperty("id", "error");
      response.addProperty("message", message);
      session.sendMessage(new TextMessage(response.toString()));
   } catch (IOException e) {
      log.error("Exception sending message", e);
   }
}
Client-Side Logic

Let’s move now to the client-side of the application. To call the previously created WebSocket service in the server-side, we use the JavaScript class WebSocket. We use a specific Kurento JavaScript library called kurento-utils.js to simplify the WebRTC interaction with the server. This library depends on adapter.js, which is a JavaScript WebRTC utility maintained by Google that abstracts away browser differences. Finally jquery.js is also needed in this application.

These libraries are linked in the index.html web page, and are used in the index.js. In the following snippet we can see the creation of the WebSocket (variable ws) in the path /repository. Then, the onmessage listener of the WebSocket is used to implement the JSON signaling protocol in the client-side. Notice that there are three incoming messages to client: startResponse, playResponse, playEnd,``error``, and iceCandidate. Convenient actions are taken to implement each step in the communication. For example, in functions start the function WebRtcPeer.WebRtcPeerSendrecv of kurento-utils.js is used to start a WebRTC communication.

var ws = new WebSocket('wss://' + location.host + '/repository');

ws.onmessage = function(message) {
   var parsedMessage = JSON.parse(message.data);
   console.info('Received message: ' + message.data);

   switch (parsedMessage.id) {
   case 'startResponse':
      startResponse(parsedMessage);
      break;
   case 'playResponse':
      playResponse(parsedMessage);
      break;
   case 'playEnd':
      playEnd();
      break;
   case 'error':
      setState(NO_CALL);
      onError('Error message from server: ' + parsedMessage.message);
      break;
   case 'iceCandidate':
      webRtcPeer.addIceCandidate(parsedMessage.candidate, function(error) {
         if (error)
            return console.error('Error adding candidate: ' + error);
      });
      break;
   default:
      setState(NO_CALL);
   onError('Unrecognized message', parsedMessage);
   }
}

function start() {
console.log('Starting video call ...');

// Disable start button
setState(DISABLED);
showSpinner(videoInput, videoOutput);

console.log('Creating WebRtcPeer and generating local sdp offer ...');

var options = {
   localVideo : videoInput,
   remoteVideo : videoOutput,
   onicecandidate : onIceCandidate
}
webRtcPeer = new kurentoUtils.WebRtcPeer.WebRtcPeerSendrecv(options,
      function(error) {
         if (error)
            return console.error(error);
         webRtcPeer.generateOffer(onOffer);
      });
}

function onOffer(error, offerSdp) {
   if (error)
      return console.error('Error generating the offer');
   console.info('Invoking SDP offer callback function ' + location.host);
   var message = {
         id : 'start',
         sdpOffer : offerSdp,
         mode :  $('input[name="mode"]:checked').val()
   }
   sendMessage(message);
}

function onError(error) {
   console.error(error);
}

function onIceCandidate(candidate) {
   console.log('Local candidate' + JSON.stringify(candidate));

   var message = {
         id : 'onIceCandidate',
         candidate : candidate
   };
   sendMessage(message);
}

function startResponse(message) {
   setState(IN_CALL);
   console.log('SDP answer received from server. Processing ...');

   webRtcPeer.processAnswer(message.sdpAnswer, function(error) {
      if (error)
         return console.error(error);
   });
}

function stop() {
   var stopMessageId = (state == IN_CALL) ? 'stop' : 'stopPlay';
   console.log('Stopping video while in ' + state + '...');
   setState(POST_CALL);
   if (webRtcPeer) {
      webRtcPeer.dispose();
      webRtcPeer = null;

      var message = {
            id : stopMessageId
      }
      sendMessage(message);
   }
   hideSpinner(videoInput, videoOutput);
}

function play() {
   console.log("Starting to play recorded video...");

   // Disable start button
   setState(DISABLED);
   showSpinner(videoOutput);

   console.log('Creating WebRtcPeer and generating local sdp offer ...');

   var options = {
      remoteVideo : videoOutput,
      onicecandidate : onIceCandidate
   }
   webRtcPeer = new kurentoUtils.WebRtcPeer.WebRtcPeerRecvonly(options,
         function(error) {
            if (error)
               return console.error(error);
            webRtcPeer.generateOffer(onPlayOffer);
         });
}

function onPlayOffer(error, offerSdp) {
   if (error)
      return console.error('Error generating the offer');
   console.info('Invoking SDP offer callback function ' + location.host);
   var message = {
         id : 'play',
         sdpOffer : offerSdp
   }
   sendMessage(message);
}

function playResponse(message) {
   setState(IN_PLAY);
   webRtcPeer.processAnswer(message.sdpAnswer, function(error) {
      if (error)
         return console.error(error);
   });
}

function playEnd() {
   setState(POST_CALL);
   hideSpinner(videoInput, videoOutput);
}

function sendMessage(message) {
   var jsonMessage = JSON.stringify(message);
   console.log('Senging message: ' + jsonMessage);
   ws.send(jsonMessage);
}
Dependencies

This Java Spring application is implemented using Maven. The relevant part of the pom.xml is where Kurento dependencies are declared. As the following snippet shows, we need two dependencies: the Kurento Client Java dependency (kurento-client) and the JavaScript Kurento utility library (kurento-utils) for the client-side. Other client libraries are managed with webjars:

<dependencies>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-client</artifactId>
   </dependency>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-utils-js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars</groupId>
      <artifactId>webjars-locator</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>bootstrap</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>demo-console</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>adapter.js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>jquery</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>ekko-lightbox</artifactId>
   </dependency>
</dependencies>

注解

We are in active development. You can find the latest version of Kurento Java Client at Maven Central.

Kurento Java Client has a minimum requirement of Java 7. Hence, you need to include the following properties in your pom:

<maven.compiler.target>1.7</maven.compiler.target>
<maven.compiler.source>1.7</maven.compiler.source>

WebRTC statistics

This tutorial implements a WebRTC loopback and shows how to collect WebRTC statistics.

JavaScript - Loopback stats

This web application extends the Hello World tutorial showing how statistics are collected.

For the impatient: running this example

You’ll need to install Kurento Media Server before running this example. Read installation guide for further information.

Be sure to have installed Node.js and Bower in your system. In an Ubuntu machine, you can install both as follows:

curl -sL https://deb.nodesource.com/setup_4.x | sudo bash -
sudo apt-get install -y nodejs
sudo npm install -g bower

Due to Same-origin policy, this demo has to be served by an HTTP server. A very simple way of doing this is by means of an HTTP Node.js server which can be installed using npm :

sudo npm install http-server -g

Clone source code from GitHub and then start the HTTP server:

git clone https://github.com/Kurento/kurento-tutorial-js.git
cd kurento-tutorial-js/kurento-loopback-stats
git checkout 6.6.1
bower install
http-server -p 8443 -S -C keys/server.crt -K keys/server.key

Connect to URL https://localhost:8443/ using a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the parameter ws_uri to the URL, as follows:

https://localhost:8443/index.html?ws_uri=wss://kms_host:kms_port/kurento

Notice that the Kurento Media Server must connected using a Secure WebSocket (i.e., the KMS URI starts with wss://). For this reason, the support for secure WebSocket must be enabled in the Kurento Media Server you are using to run this tutorial. For further information about securing applications, please visit the following page.

Understanding this example

The logic of the application is quite simple: the local stream is sent to the Kurento Media Server, which returns it back to the client without modifications. To implement this behavior we need to create a Media Pipeline composed by the Media Element WebRtcEndpoint, which holds the capability of exchanging full-duplex (bidirectional) WebRTC media flows. This media element is connected to itself so any received media (from browser) is send back (to browser). Using method getStats the application shows all stats of element WebRtcEndpoint.

The complete source code of this demo can be found in GitHub.

JavaScript Logic

This demo follows a Single Page Application architecture (SPA). The interface is the following HTML page: index.html. This web page links two Kurento JavaScript libraries:

  • kurento-client.js : Implementation of the Kurento JavaScript Client.
  • kurento-utils.js : Kurento utility library aimed to simplify the WebRTC management in the browser.

In addition, these two JavaScript libraries are also required:

  • Bootstrap : Web framework for developing responsive web sites.
  • jquery.js : Cross-platform JavaScript library designed to simplify the client-side scripting of HTML.
  • adapter.js : WebRTC JavaScript utility library maintained by Google that abstracts away browser differences.
  • ekko-lightbox : Module for Bootstrap to open modal images, videos, and galleries.
  • demo-console : Custom JavaScript console.

The specific logic of this demo is coded in the following JavaScript page: index.js. In this file, there is a function which is called when the green button labeled as Start in the GUI is clicked.

var startButton = document.getElementById("start");

startButton.addEventListener("click", function() {
   var options = {
     localVideo: videoInput,
     remoteVideo: videoOutput
   };

   webRtcPeer = kurentoUtils.WebRtcPeer.WebRtcPeerSendrecv(options, function(error) {
      if(error) return onError(error)
      this.generateOffer(onOffer)
   });

   [...]
}

The function WebRtcPeer.WebRtcPeerSendrecv hides internal details (i.e. PeerConnection and getUserStream) and makes possible to start a full-duplex WebRTC communication, using the HTML video tag with id videoInput to show the video camera (local stream) and the video tag videoOutput to show the remote stream provided by the Kurento Media Server.

Inside this function, a call to generateOffer is performed. This function accepts a callback in which the SDP offer is received. In this callback we create an instance of the KurentoClient class that will manage communications with the Kurento Media Server. So, we need to provide the URI of its WebSocket endpoint. In this example, we assume it’s listening in port 8433 at the same host than the HTTP serving the application.

[...]

var args = getopts(location.search,
{
  default:
  {
    ws_uri: 'wss://' + location.hostname + ':8433/kurento',
    ice_servers: undefined
  }
});

[...]

kurentoClient(args.ws_uri, function(error, client){
  [...]
};

Once we have an instance of kurentoClient, the following step is to create a Media Pipeline, as follows:

client.create("MediaPipeline", function(error, _pipeline){
   [...]
});

If everything works correctly, we have an instance of a media pipeline (variable pipeline in this example). With this instance, we are able to create Media Elements. In this example we just need a WebRtcEndpoint. Then, this media elements is connected itself:

pipeline.create("WebRtcEndpoint", function(error, webRtc) {
   if (error) return onError(error);

   webRtcEndpoint = webRtc;

   setIceCandidateCallbacks(webRtcPeer, webRtc, onError)

   webRtc.processOffer(sdpOffer, function(error, sdpAnswer) {
     if (error) return onError(error);

     webRtc.gatherCandidates(onError);

     webRtcPeer.processAnswer(sdpAnswer, onError);
   });

   webRtc.connect(webRtc, function(error) {
     if (error) return onError(error);

     console.log("Loopback established");

     webRtcEndpoint.on('MediaStateChanged', function(event) {
       if (event.newState == "CONNECTED") {
         console.log("MediaState is CONNECTED ... printing stats...")
         activateStatsTimeout();
       }
     });
   });
});

In the following snippet, we can see getStats method. This method returns several statistic values of WebRtcEndpoint.

function getBrowserOutgoingVideoStats(webRtcPeer, callback) {
  var peerConnection = webRtcPeer.peerConnection;

  peerConnection.getStats(function(stats) {
    var results = stats.result();

    for (var i = 0; i < results.length; i++) {
      var res = results[i];
      if (res.type != 'ssrc') continue;

      //Publish it to be compliant with W3C stats draft
      var retVal = {
        timeStamp: res.timestamp,
        //StreamStats below
        associateStatsId: res.id,
        codecId: "--",
        firCount: res.stat('googFirsReceived'),
        isRemote: false,
        mediaTrackId: res.stat('googTrackId'),
        nackCount: res.stat('googNacksReceived'),
        pliCount: res.stat('googPlisReceived'),
        sliCount: 0,
        ssrc: res.stat('ssrc'),
        transportId: res.stat('transportId'),
        //Specific outbound below
        bytesSent: res.stat('bytesSent'),
        packetsSent: res.stat('packetsSent'),
        roundTripTime: res.stat('googRtt'),
        packetsLost: res.stat('packetsLost'),
        targetBitrate: "??",
        remb: "??"
      }
      return callback(null, retVal);
    }
    return callback("Error: could not find ssrc type on track stats", null);
  }, localVideoTrack);
}

注解

The TURN and STUN servers to be used can be configured simple adding the parameter ice_servers to the application URL, as follows:

https://localhost:8443/index.html?ice_servers=[{"urls":"stun:stun1.example.net"},{"urls":"stun:stun2.example.net"}]
https://localhost:8443/index.html?ice_servers=[{"urls":"turn:turn.example.org","username":"user","credential":"myPassword"}]
Dependencies

Demo dependencies are located in file bower.json. Bower is used to collect them.

"dependencies": {
   "kurento-client": "6.6.0",
   "kurento-utils": "6.6.2"
}

注解

We are in active development. You can find the latest version of Kurento JavaScript Client at Bower.

精通 Kurento

Kurento Architecture

Kurento Architecture

Kurento, as most multimedia communication technologies out there, is built using two layers (called planes) to abstract key functions in all interactive communication systems:

  • Signaling Plane. The parts of the system in charge of the management of communications, that is, the modules that provides functions for media negotiation, QoS parametrization, call establishment, user registration, user presence, etc. are conceived as forming part of the Signaling Plane.
  • Media Plane Functionalities such as media transport, media encoding/decoding and media processing make the Media Plane, which takes care of the handling of media. The distinction comes from the telephony differentiation between the handling of voice and the handling of meta-information such as tone, billing, etc.

The following figure shows a conceptual representation of the high level architecture of Kurento.

Kurento Architecture

Kurento Architecture. Kurento architecture follows the traditional separation between signaling and media planes.

The right side of the picture shows the application, which is in charge of the signaling plane and contains the business logic and connectors of the particular multimedia application being deployed. It can be build with any programming technology like Java, Node.js, PHP, Ruby, .NET, etc. The application can use mature technologies such as HTTP and SIP Servlets, Web Services, database connectors, messaging services, etc. Thanks to this, this plane provides access to the multimedia signaling protocols commonly used by end-clients such as SIP, RESTful and raw HTTP based formats, SOAP, RMI, CORBA or JMS. These signaling protocols are used by client side of applications to command the creation of media sessions and to negotiate their desired characteristics on their behalf. Hence, this is the part of the architecture, which is in contact with application developers and, for this reason, it needs to be designed pursuing simplicity and flexibility.

On the left side, we have the Kurento Media Server, which implements the media plane capabilities providing access to the low-level media features: media transport, media encoding/decoding, media transcoding, media mixing, media processing, etc. The Kurento Media Server must be capable of managing the multimedia streams with minimal latency and maximum throughput. Hence the Kurento Media Server must be optimized for efficiency.

Kurento APIs and interfaces

The capabilities of the media plane (Kurento Media Server) and signaling plane (Application) are exposed through a number of APIs, which provide increasing abstraction levels.

Following this, the role of the different APIs can be summarized in the following way:

  • Kurento Protocol: Is a network protocol exposing the Kurento Media Server capabilities through WebSocket (read more in Kurento Protocol section).
  • Kurento API: Is the object oriented view of the Kurento Protocol. This API makes possible the creation and management of media elements and pipelines by using references (ids). Accessing the Kurento API is possible from any of the computer languages and frameworks implementing Kurento Protocol. (read more in Kurento API section)
  • Kurento Java Client: Is a Java SE layer which consumes the Kurento API and exposes its capabilities through a simple-to-use modularity based on Java POJOs representing media elements and media pipelines. This API is abstract in the sense that all the non-intuitive inherent complexities of the internal Kurento Protocol workings are abstracted and developers do not need to deal with them when creating applications. Using the Kurento Java Client only requires adding the appropriate dependency to a maven project or to download the corresponding jar into the application developer CLASSPATH. It is important to remark that the Kurento Java Client is a media-plane control API. In other words, its objective is to expose the capability of managing media objects, but it does not provide any signaling plane capabilities.
  • Kurento JavaScript Client: Is a JavaScript layer which consumes the Kurento API and exposes its capabilities to JavaScript developers. It allow to build node.js and browser based applications. In the future, further Kurento Clients can be created exposing the same kind of modularity in other languages such as Python, C/C++, PHP, etc.

From an architectural perspective, the only relevant aspect is that application developers can use Kurento Clients or Kurento API directly for creating their multimedia enabled applications. This opens a wide spectrum of potential usage scenarios ranging from web applications (written using the Kurento JavaScript client), desktop applications (written using the Kurento Java Client), distibuted applications (writen using Kurento Protocol, etc.).

Kurento Modules

Kurento has been designed as a pluggable framework. Kurento Media Server uses several modules by default, named kms-core, kms-elements and kms-filters. In addition, there are others built-in modules to enhance the capabilities provided by the Kurento Media Server. These modules are called kms-crowddetector, kms-pointerdetector, kms-chroma, and kms-platedetector. Finally Kurento Media Server can be expanded with new custom modules.

Kurento modules architecture

Kurento modules architecture. Kurento Media Server can be extended with built-it modules (crowddetector, pointerdetector, chroma, platedetector) and also with other custom modules.

For further details please visit the Kurento Modules page.

Creating applications with Kurento

Kurento can be used following the architectural principles of the WWW. That is, creating a multimedia applications basing on it can be a similar experience to creating a web application using any of the popular web development frameworks.

At the highest abstraction level, web applications have an architecture comprised of three different layers:

  • Presentation layer (client side): Here we can find all the application code which is in charge of interacting with end users so that information is represented in a comprehensive way user input is captured. This usually consists on HTML pages.
  • Application logic (server side): This layer is in charge of implementing the specific functions executed by the application.
  • Service layer (server or Internet side): This layer provides capabilities used by the application logic such as databases, communications, security, etc. This services can be hosted in the same server as application logic or can be provided by external parties.

Following this parallelism, multimedia applications created using Kurento can also be implemented with the same architecture:

  • Presentation layer (client side): Is in charge of multimedia representation and multimedia capture. It is usually based on specific build-in capabilities of the client. For example, when creating a browser-based application, the presentation layer will use capabilities such as the <video> HTML tag or the WebRTC JavaScript APIs.
  • Application logic: This layer provides the specific multimedia logic. In other words, this layer is in charge of building the appropriate pipeline (by chaining the desired media elements) that the multimedia flows involved in the application will need to traverse.
  • Service layer: This layer provides the multimedia services that support the application logic such as media recording, media ciphering, etc. The Kurento Media Server (i.e. the specific pipeline of media elements) is in charge of this layer.

The interesting aspect of this discussion is that, as happens with WWW development, Kurento applications can place the Presentation layer at the client side and the Service layer at the server side. However, the Application Logic layer, in both cases, can be located at either of the sides or even distributed between them. This idea is represented in the following picture:

Layered architecture of web and multimedia applications

Layered architecture of web and multimedia applications. Applications created using Kurento (right) can be similar to standard WWW applications (left). Both types of applications may choose to place the application logic at the client or at the server code.

This means that Kurento developers can choose to include the code creating the specific media pipeline required by their applications at the client side (using a suitable Kurento Client or directly with Kurento Protocol) or can place it at the server side.

Both options are valid but each of them drives to different development styles. Having said this, it is important to note that in the WWW developers usually tend to maintain client side code as simple as possible, bringing most of their application logic to the server. Reproducing this kind of development experience is the most usual way of using Kurento. That is, by locating the multimedia application logic at the server side, so that the specific media pipelines are created using the Kurento Client for your favorite language.

注解

In the following sections it is considered that all Kurento handling is done at the server side. Although this is the most common way of using Kurento, is important to note that all multimedia logic can be implemented at the client with Kurento JavaScript Client.

Communicating client, server and Kurento

As can be observed in Figure above, a Kurento application involves interactions among three main modules:

  • Client Application: which involves the native multimedia capabilities of the client platform plus the specific client-side application logic. It can use Kurento Clients designed to client platforms (for example, Kurento JavaScript Client).
  • Application Server: which involves an application server and the server-side application logic. It can use Kurento Clients designed to server platforms (for example, Kurento Java Client for Java EE and Kurento JavaScript Client for Node.js).
  • Kurento Media Server: which receives commands for creating specific multimedia capabilities (i.e. specific pipelines adapted to the needs of specific applications)

The interactions maintained among these modules depend on the specificities of each application. However, in general, for most applications they can be reduced to the following conceptual scheme:

Main interactions between architectural modules

Main interactions between architectural modules. Main interactions occur in two phases: negotiation and media exchange. Remark that the color of the different arrows and boxes is aligned with the architectural figures presented above, so that, for example, orange arrows show exchanges belonging to the signaling plane, blue arrows show exchanges belonging to the Kurento Protocol, red boxes are associated to the Kurento Media Server and green boxes with the application.

1. Media negotiation phase (signaling)

As it can be observed, at a first stage, a client (a browser in a computer, a mobile application, etc.) issues a message to the application requesting some kind of multimedia capability. This message can be implemented with any protocol (http, websockets, SIP, etc.). For instance, that request could ask for the visualization of a given video clip.

When the application receives the request, if appropriate, it will carry out the specific server side application logic, which can include Authentication, Authorization and Accounting (AAA), CDR generation, consuming some type of web service, etc.

After that, the application processes the request and, according to the specific instructions programmed by the developer, commands Kurento Media Server to instantiate the suitable media elements and to chain them in an appropriate media pipeline. Once the pipeline has been created successfully, kurento Media server responds accordingly and the application forwards the successful response to the client, showing it how and where the media service can be reached.

During the above mentioned steps no media data is really exchanged. All the interactions have the objective of negotiating the whats, hows, wheres and whens of the media exchange. For this reason, we call it the negotiation phase. Clearly, during this phase only signaling protocols are involved.

2. Media exchange phase

After that, a new phase starts devoted to producing the actual media exchange. The client addresses a request for the media to the Kurento Media Server using the information gathered during the negotiation phase. Following with the video-clip visualization example mentioned above, the browser will send a GET request to the IP address and port of the Kurento Media Server where the clip can be obtained and, as a result, an HTTP reponse with the media will be received.

Following the discussion with that simple example, one may wonder why such a complex scheme for just playing a video, when in most usual scenarios clients just send the request to the appropriate URL of the video without requiring any negotiation. The answer is straightforward. Kurento is designed for media applications involving complex media processing. For this reason, we need to establish a two-phase mechanism enabling a negotiation before the media exchange. The price to pay is that simple applications, such as one just downloading a video, also need to get through these phases. However, the advantage is that when creating more advanced services the same simple philosophy will hold. For example, if we want to add augmented reality or computer vision features to that video-clip, we just need to create the appropriate pipeline holding the desired media element during the negotiation phase. After that, from the client perspective, the processed clip will be received as any other video.

Real time WebRTC applications with Kurento

Kurento allows the establishment of real time multimedia session between a browser and the Kurento Media Server directly through the use of WebRTC. In addition, Kurento Media Server can be used to act as media proxy for making possible the communication among different clients, which are mediated by the kurento infrastructure. Hence, Kurento Media Server can act as a conference bridge (Multi-Conference Unit, MCU), as a machine-to-machine communication system, as a video call recording system, etc.

As shown in the picture, the client exposes its media capabilities through an SDP (Session Description Protocol) sent in a request. Hence, the application is able to instantiate the appropriate WebRTC endpoint, and to require it to generate a response SDP based on its own capabilities and on the offered SDP. When the answer SDP is obtained, it is given back to the client and the media exchange can be started. The interactions among the different modules are summarized in the following picture

Main interactions in a RTC session

Main interactions in a WebRTC session. Interactions taking place in a Real Time Communications (RTC) session. During the negotiation phase, a Session Description Protocol (SDP) message is exchanged offering the capabilities of the client. As a result, Kurento Media Server generates an SDP answer that can be used by the client for extablishing the media exchange.

The application developer is able to create the desired pipeline during the negotiation phase, so that the real time multimedia stream is processed accordingly to the application needs. Just as an example, imagine that we want to create a WebRTC application recording the media received from the client and augmenting it so that if a human face is found, a hat will be rendered on top of it. This pipeline is schematically shown in the figure below, where we assume that the Filter element is capable of detecting the face and adding the hat to it.

Example pipeline for a WebRTC session

Example pipeline for a WebRTC session. During the negotiation phase, the application developer can create a pipeline providing the desired specific functionality. For example, this pipeline uses a WebRtcEndpoint for communicating with the client, which is connected to a RecorderEndpoint storing the received media streamd and to an augmented reality filter, which feeds its output media stream back to the client. As a result, the end user will receive its own image filtered (e.g. with a hat added onto her head) and the stream will be recorded and made available for further recovery into a repository (e.g. a file).

Kurento Design Principles

Kurento is designed based on the following main principles:

Separate Media and Signaling Planes
Signaling and Media are two separate planes and Kurento is designed so that applications can handle separately those facets of multimedia processing.
Distribution of Media and Application Services

Kurento Media Server and applications can be collocated, scalated or distributed among different machines.

A single application can invoke the services of more than one Kurento Media Server. The opposite also applies, that is, a Kurento Media Server can attend the requests of more than one application.

Suitable for the Cloud
Kurento is suitable to be integrated into cloud environments to act as a PaaS (Platform as a Service) component.
Media Pipelines
Chaining Media Elements via Media Pipelines is an intuitive approach to challenge the complexity of multimedia processing.
Application development
Developers do not need to be aware of internal Kurento Media Server complexities, all the applications can deployed in any technology or framework the developer like, from client to server. From browsers to cloud services.
End-to-end Communication Capability
Kurento provides end-to-end communication capabilities so developers do not need to deal with the complexity of transporting, encoding/decoding and rendering media on client devices.
Fully Processable Media Streams
Kurento enables not only interactive interpersonal communications (e.g. Skype-like with conversational call push/reception capabilities), but also human-to-machine (e.g. Video on Demand through real-time streaming) and machine-to-machine (e.g. remote video recording, multisensory data exchange) communications.
Modular Processing of Media
Modularization achieved through media elements and pipelines allows defining the media processing functionality of an application through a “graph-oriented” language, where the application developer is able to create the desired logic by chaining the appropriate functionalities.
Auditable Processing
Kurento is able to generate rich and detailed information for QoS monitoring, billing and auditing.
Seamless IMS integration
Kurento is designed to support seamless integration into the IMS infrastructure of Telephony Carriers.
Transparent Media Adaptation Layer
Kurento provides a transparent media adaptation layer to make the convergence among different devices having different requirements in terms of screen size, power consumption, transmission rate, etc. possible.

Kurento API Reference

Kurento API Reference

Kurento Media Server exposes an API to high level languages that allow application programmers to control it. This high level API can be used with a Kurento Client for Java or JavaScript. If you prefer another programming language, you can use the Kurento Protocol, based on WebSocket and JSON-RPC.

In the following sections we will describe the Kurento API in a high level way. We will show the media capabilities exposed by Kurento Media Server to clients. If you want see working demos using Kurento, please refer to Tutorials section.

Media elements and media pipelines

Kurento is based on two concepts that act as building blocks for application developers:

  • Media Elements. A Media element is a functional unit performing a specific action on a media stream. Media elements are a way of every capability is represented as a self-contained “black box” (the media element) to the application developer, who does not need to understand the low-level details of the element for using it. Media elements are capable of receiving media from other elements (through media sources) and of sending media to other elements (through media sinks). Depending on their function, media elements can be split into different groups:
    • Input Endpoints: Media elements capable of receiving media and injecting it into a pipeline. There are several types of input endpoints. File input endpoints take the media from a file, Network input endpoints take the media from the network, and Capture input endpoints are capable of capturing the media stream directly from a camera or other kind of hardware resource.
    • Filters: Media elements in charge of transforming or analyzing media. Hence there are filters for performing operations such as mixing, muxing, analyzing, augmenting, etc.
    • Hubs: Media Objects in charge of managing multiple media flows in a pipeline. A Hub has several hub ports where other media elements are connected. Depending on the Hub type, there are different ways to control the media. For example, there are a Hub called Composite that merge all input video streams in a unique output video stream with all inputs in a grid.
    • Output Endpoints: Media elements capable of taking a media stream out of the pipeline. Again, there are several types of output endpoints specialized in files, network, screen, etc.
  • Media Pipeline: A Media Pipeline is a chain of media elements, where the output stream generated by one element (source) is fed into one or more other elements input streams (sinks). Hence, the pipeline represents a “machine” capable of performing a sequence of operations over a stream.
Media Pipeline Example

Example of a Media Pipeline implementing an interactive multimedia application receiving media from a WebRtcEndpoint, overlaying and image on the detected faces and sending back the resulting stream

Kurento API is an object oriented API. That is, there are classes that can be instantiated. This classes define operations that can be invoked over objects of this classes. The classes can have an inheritance relationship with other classes, inheriting operations from parent classes to children ones.

The following class diagram shows some of the relationships of the main classes in the Kurento API.

Class diagram of main classes in Kurento API

Class diagram of main classes in Kurento API

Endpoints

Let us discuss briefly the different Endpoints offered by kurento.

A WebRtcEndpoint is an output and input endpoint that provides media streaming for Real Time Communications (RTC) through the web. It implements WebRTC technology to communicate with browsers.

_images/WebRtcEndpoint.png

A RtpEndpoint is an output and input endpoint. That is, provides bidirectional content delivery capabilities with remote networked peers through RTP protocol. As you can imagine, to send and receive media through the network it uses RTP protocol and SDP for media negotiation.

_images/RtpEndpoint.png

An HttpPostEndpoint is an input endpoint that accepts media using http POST requests like HTTP file upload function.

_images/HttpPostEndpoint.png

A PlayerEndpoint is an input endpoint that retrieves content from file system, http URL or RTSP url and inject it into the media pipeline.

_images/PlayerEndpoint.png

A RecorderEndpoint is an output endpoint that provides function to store contents in reliable mode (doesn’t discard data). It contains Media Sink pads for audio and video.

_images/RecorderEndpoint.png

The following class diagram shows the relationships of the main endpoint classes.

Class diagram of main Endpoints in Kurento API

Class diagram of main Endpoints in Kurento API

Filters

Filters are MediaElements that perform media processing, computer vision, augmented reality, and so on. Let see the available filters in Kurento:

The ZBarFilter filter detects QR and bar codes in a video stream. When a code is found, the filter raises a CodeFoundEvent. Clients can add a listener to this event to execute some action.

_images/ZBarFilter.png

The FaceOverlayFilter filter detects faces in a video stream and overlaid it with a configurable image.

_images/FaceOverlayFilter.png

GStreamerFilter is a generic filter interface that allow use GStreamer filter in Kurento Media Pipelines.

_images/GStreamerFilter.png

The following class diagram shows the relationships of the main filter classes.

Class diagram of main Filters in Kurento API

Class diagram of main Filters in Kurento API

Hubs

Hubs are media objects in charge of managing multiple media flows in a pipeline. A Hub has several hub ports where other media elements are connected. Let’s see the available hubs in Kurento:

Composite is a hub that mixes the audio stream of its connected inputs and constructs a grid with the video streams of them.

_images/Composite.png

DispatcherOneToMany is a Hub that sends a given input to all the connected output HubPorts.

_images/DispatcherOneToMany.png

Dispatcher is a hub that allows routing between arbitrary input-output HubPort pairs.

_images/Dispatcher.png

The following class diagram shows the relationships of the hubs.

Class diagram of main Hubs in Kurento API

Class diagram of main Hubs in Kurento API

You see the details of the Kurento Clients see the JavaDoc/JsDoc:

Kurento Protocol

Kurento Protocol

Kurento Media Server can be controlled by means of two out of the box Kurento Clients, i.e. Java or JavaScript. These clients use the Kurento Protocol to speak with the KMS. Kurento Protocol is based on WebSocket and uses JSON-RPC V2.0 messages for making requests and sending responses.

JSON-RPC Messages format

Kurento Protocol uses JSON-RPC V2.0 to code its messages. The following subsections shows how to use this format in JSON messages.

Request messages

An RPC call is represented by sending a request message to a server. The request message has the following members:

  • jsonrpc: a string specifying the version of the JSON-RPC protocol. It must be exactly “2.0”.
  • id: an unique identifier established by the client that contains a string or number. The server must reply with the same value in the response message. This member is used to correlate the context between both messages.
  • method: a string containing the name of the method to be invoked.
  • params: a structured value that holds the parameter values to be used during the invocation of the method.

The following JSON shows a sample request for the creation of a PlayerEndpoint Media Element:

{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "create",
  "params": {
    "type": "PlayerEndpoint",
    "constructorParams": {
      "pipeline": "6829986",
      "uri": "http://host/app/video.mp4"
    },
    "sessionId": "c93e5bf0-4fd0-4888-9411-765ff5d89b93"
  }
}
Successful Response messages

When an RPC call is made the server replies with a response message. In the case of a successful response, the response message will contain the following members:

  • jsonrpc: a string specifying the version of the JSON-RPC protocol. It must be exactly “2.0”.
  • id: this member is mandatory and it must match the value of the id member in the request message.
  • result: its value is determined by the method invoked on the server. In case the connection is rejected, it’s returned an message with a rejected attribute containing an message with a code and message attributes with the reason why the session was not accepted, and no sessionId is defined.

The following example shows a typical successful response:

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "value": "442352747",
    "sessionId": "c93e5bf0-4fd0-4888-9411-765ff5d89b93"
  }
}
Error Response messages

When an RPC call is made the server replies with a response message. In the case of an error response, the response message will contain the following members:

  • jsonrpc: a string specifying the version of the JSON-RPC protocol. It must be exactly “2.0”.
  • id: this member is mandatory and it must match the value of the id member in the request message. If there was an error in detecting the id in the request message (e.g. Parse Error/Invalid Request), it equals to null.
  • error: an message describing the error through the following members:
    • code: an integer number that indicates the error type that occurred.
    • message: a string providing a short description of the error.
    • data: a primitive or structured value that contains additional information about the error. It may be omitted. The value of this member is defined by the server.

The following example shows a typical error response:

{
  "jsonrpc": "2.0",
  "id": 1,
  "error": {
    "code": "33",
    "message": "Invalid paramter format"
  }
}
Kurento API over JSON-RPC

As explained in Kurento API section, Kurento Media Server exposes a full fledged API to let applications to process media in several ways.

To allow this rich API, Kurento Clients require requires full-duplex communications between client and server infrastructure. For this reason, the Kurento Protocol is based on WebSocket transports.

Previous to issuing commands, the Kurento Client requires establishing a WebSocket connection with Kurento Media Server to the URL: ws://hostname:port/kurento

Once the WebSocket has been established, the Kurento Protocol offers different types of request/response messages:

  • ping: Keep-alive method between client and Kurento Media Server.
  • create: Instantiates a new media object, that is, a pipeline or media element.
  • invoke: Calls a method of an existing media object.
  • subscribe: Creates a subscription to an event in a object.
  • unsubscribe: Removes an existing subscription to an event.
  • release: Deletes the object and release resources used by it.

The Kurento Protocol allows to Kurento Media Server send requests to clients:

  • onEvent: This request is sent from Kurento Media server to clients when an event occurs.
Ping

In order to warranty the WebSocket connectivity between the client and the Kurento Media Server, a keep-alive method is implemented. This method is based on a ping method sent by the client, which must be replied with a pong message from the server. If no response is obtained in a time interval, the client is aware that the connectivity with the media server has been lost.The parameter interval is the time out to receive the Pong message from the server, in milliseconds. By default this value is 240000 (i.e. 40 seconds). This is an example of ping request:

{
    "id": 1,
    "method": "ping",
    "params": {
        "interval": 240000
    },
    "jsonrpc": "2.0"
}

The response to a ping request must contain a result object with a value parameter with a fixed name: pong. The following snippet shows the pong response to the previous ping request:

{
    "id": 1,
    "result": {
        "value": "pong"
    },
    "jsonrpc": "2.0"
}
Create

Create message requests the creation of an object of the Kurento API (Media Pipelines and Media Elements). The parameter type specifies the type of the object to be created. The parameter constructorParams contains all the information needed to create the object. Each message needs different constructorParams to create the object. These parameters are defined in Kurento API section.

Media Elements have to be contained in a previously created Media Pipeline. Therefore, before creating Media Elements, a Media Pipeline must exist. The response of the creation of a Media Pipeline contains a parameter called sessionId, which must be included in the next create requests for Media Elements.

The following example shows a request message requesting the creation of an object of the type MediaPipeline:

{
    "id": 2,
    "method": "create",
    "params": {
        "type": "MediaPipeline",
        "constructorParams": {},
        "properties": {}
    },
    "jsonrpc": "2.0"
}

The response to this request message is as follows. Notice that the parameter value identifies the created Media Pipelines, and sessionId is the identifier of the current session:

{
    "id": 2,
    "result": {
        "value": "6ba9067f-cdcf-4ea6-a6ee-d74519585acd_kurento.MediaPipeline",
        "sessionId": "bd4d6227-0463-4d52-b1c3-c71f0be68466"
    },
    "jsonrpc": "2.0"
}

The response message contains the identifier of the new object in the field value. As usual, the message id must match with the request message. The sessionId is also returned in each response. The following example shows a request message requesting the creation of an object of the type WebRtcEndpoint within an existing Media Pipeline (identified by the parameter mediaPipeline). Notice that in this request, the sessionId is already present, while in the previous example it was not (since at that point was unknown for the client):

{
    "id": 3,
    "method": "create",
    "params": {
        "type": "WebRtcEndpoint",
        "constructorParams": {
            "mediaPipeline": "6ba9067f-cdcf-4ea6-a6ee-d74519585acd_kurento.MediaPipeline"
        },
        "properties": {},
        "sessionId": "bd4d6227-0463-4d52-b1c3-c71f0be68466"
    },
    "jsonrpc": "2.0"
}

The following example shows a request message requesting the creation of an object of the type WebRtcEndpoint within an existing Media Pipeline (identified by the parameter mediaPipeline). Notice that in this request, the sessionId is already present, while in the previous example it was not (since at that point was unknown for the client):

{
    "id": 3,
    "result": {
        "value": "6ba9067f-cdcf-4ea6-a6ee-d74519585acd_kurento.MediaPipeline/087b7777-aab5-4787-816f-f0de19e5b1d9_kurento.WebRtcEndpoint",
        "sessionId": "bd4d6227-0463-4d52-b1c3-c71f0be68466"
    },
    "jsonrpc": "2.0"
}
Invoke

Invoke message requests the invocation of an operation in the specified object. The parameter object indicates the id of the object in which the operation will be invoked. The parameter operation carries the name of the operation to be executed. Finally, the parameter operationParams has the parameters needed to execute the operation.

The following example shows a request message requesting the invocation of the operation connect on a PlayerEndpoint connected to a WebRtcEndpoint:

{
    "id": 5,
    "method": "invoke",
    "params": {
        "object": "6ba9067f-cdcf-4ea6-a6ee-d74519585acd_kurento.MediaPipeline/76dcb8d7-5655-445b-8cb7-cf5dc91643bc_kurento.PlayerEndpoint",
        "operation": "connect",
        "operationParams": {
            "sink": "6ba9067f-cdcf-4ea6-a6ee-d74519585acd_kurento.MediaPipeline/087b7777-aab5-4787-816f-f0de19e5b1d9_kurento.WebRtcEndpoint"
        },
        "sessionId": "bd4d6227-0463-4d52-b1c3-c71f0be68466"
    },
    "jsonrpc": "2.0"
}

The response message contains the value returned while executing the operation invoked in the object or nothing if the operation doesn’t return any value.

The following example shows a typical response while invoking the operation connect (that doesn’t return anything):

{
    "id": 5,
    "result": {
        "sessionId": "bd4d6227-0463-4d52-b1c3-c71f0be68466"
    },
    "jsonrpc": "2.0"
}
Release

Release message requests the release of the specified object. The parameter object indicates the id of the object to be released:

{
    "id": 36,
    "method": "release",
    "params": {
        "object": "6ba9067f-cdcf-4ea6-a6ee-d74519585acd_kurento.MediaPipeline",
        "sessionId": "bd4d6227-0463-4d52-b1c3-c71f0be68466"
    },
    "jsonrpc": "2.0"
}

The response message only contains the sessionId. The following example shows the typical response of a release request:

{
    "id": 36,
    "result": {
        "sessionId": "bd4d6227-0463-4d52-b1c3-c71f0be68466"
    },
    "jsonrpc": "2.0"
}
Subscribe

Subscribe message requests the subscription to a certain kind of events in the specified object. The parameter object indicates the id of the object to subscribe for events. The parameter type specifies the type of the events. If a client is subscribed for a certain type of events in an object, each time an event is fired in this object, a request with method onEvent is sent from Kurento Media Server to the client. This kind of request is described few sections later.

The following example shows a request message requesting the subscription of the event type EndOfStream on a PlayerEndpoint object:

{
    "id": 11,
    "method": "subscribe",
    "params": {
        "type": "EndOfStream",
        "object": "6ba9067f-cdcf-4ea6-a6ee-d74519585acd_kurento.MediaPipeline/76dcb8d7-5655-445b-8cb7-cf5dc91643bc_kurento.PlayerEndpoint",
        "sessionId": "bd4d6227-0463-4d52-b1c3-c71f0be68466"
    },
    "jsonrpc": "2.0"
}

The response message contains the subscription identifier. This value can be used later to remove this subscription.

The following example shows the response of subscription request. The value attribute contains the subscription id:

{
    "id": 11,
    "result": {
        "value": "052061c1-0d87-4fbd-9cc9-66b57c3e1280",
        "sessionId": "bd4d6227-0463-4d52-b1c3-c71f0be68466"
    },
    "jsonrpc": "2.0"
}
Unsubscribe

Unsubscribe message requests the cancellation of a previous event subscription. The parameter subscription contains the subscription id received from the server when the subscription was created.

The following example shows a request message requesting the cancellation of the subscription 353be312-b7f1-4768-9117-5c2f5a087429 for a given object:

{
    "id": 38,
    "method": "unsubscribe",
    "params": {
        "subscription": "052061c1-0d87-4fbd-9cc9-66b57c3e1280",
        "object": "6ba9067f-cdcf-4ea6-a6ee-d74519585acd_kurento.MediaPipeline/76dcb8d7-5655-445b-8cb7-cf5dc91643bc_kurento.PlayerEndpoint",
        "sessionId": "bd4d6227-0463-4d52-b1c3-c71f0be68466"
    },
    "jsonrpc": "2.0"
}

The response message only contains the sessionId. The following example shows the typical response of an unsubscription request:

{
    "id": 38,
    "result": {
        "sessionId": "bd4d6227-0463-4d52-b1c3-c71f0be68466"
    },
    "jsonrpc": "2.0"
}
OnEvent

When a client is subscribed to a type of events in an object, the server sends an onEvent request each time an event of that type is fired in the object. This is possible because the Kurento Protocol is implemented with WebSockets and there is a full duplex channel between client and server. The request that server send to client has all the information about the event:

  • source: the object source of the event.
  • type: The type of the event.
  • timestamp: Date and time of the media server.
  • tags: Media elements can be labeled using the methods setSendTagsInEvents and addTag present in each element. These tags are key-value metadata that can be used by developers for custom purposes. Tags are returned with each event by the media server in this field.

The following example shows a notification sent for server to client to notify an event of type EndOfStream for a PlayerEndpoint object:

{
  "jsonrpc":"2.0",
  "method":"onEvent",
  "params":{
     "value":{
        "data":{
           "source":"681f1bc8-2d13-4189-a82a-2e2b92248a21_kurento.MediaPipeline/e983997e-ac19-4f4b-9575-3709af8c01be_kurento.PlayerEndpoint",
           "tags":[],
           "timestamp":"1441277150",
           "type":"EndOfStream"
        },
        "object":"681f1bc8-2d13-4189-a82a-2e2b92248a21_kurento.MediaPipeline/e983997e-ac19-4f4b-9575-3709af8c01be_kurento.PlayerEndpoint",
        "type":"EndOfStream"
     }
   }
}

Notice that this message has no id field due to the fact that no response is required.

Network issues

Resources handled by KMS are high-consuming. For this reason, KMS implements a garbage collector.

A Media Element is collected when the client is disconnected longer than 4 minutes. After that time, these media elements are disposed automatically.

Therefore the WebSocket connection between client and KMS be active any time. In case of temporary network disconnection, KMS implements a mechanism to allow the client reconnection.

There is an special kind of message with the format above. This message allows a client to reconnect to the same KMS previously connected:

{
  "jsonrpc": "2.0",
  "id": 7,
  "method": "connect",
  "params": {
    "sessionId":"4f5255d5-5695-4e1c-aa2b-722e82db5260"
  }
}

If KMS replies as follows:

{
  "jsonrpc": "2.0",
  "id": 7,
  "result": {
    "sessionId":"4f5255d5-5695-4e1c-aa2b-722e82db5260"
  }
}

... this means that client is reconnected to the same KMS. In case of reconnection to another KMS, the message is the following:

{
   "jsonrpc":"2.0",
   "id": 7,
   "error":{
     "code":40007,
     "message":"Invalid session",
     "data":{
        "type":"INVALID_SESSION"
     }
   }
}

In this case client is supposed to invoke the connect primitive once again in order to get a new sessionId:

{
   "jsonrpc":"2.0",
   "id": 7,
   "method":"connect"
}
Kurento API

In order to implement a Kurento client you need the reference documentation. The best way to know all details is take a look to IDL file that defines the interface of the Kurento elements. We have defined a custom IDL format based on JSON. From it, we generate the client code for Java and JavaScript. Kurento API is defined in the following IDL files:

Example: WebRTC in loopback

This section describes an example of the messages interchanged between a Kurento client and the Kurento Media Server in order to create a WebRTC in loopback. This example is fully depicted in the tutorials section. The steps are the following:

  1. Client sends a request message in order to a media pipeline:

    {
  "id":1,
  "method":"create",
  "params":{
     "type":"MediaPipeline",
     "constructorParams":{},
     "properties":{}
  },
  "jsonrpc":"2.0"
}

2. KMS sends a response message with the identifier for the media pipeline and the media session:

{
  "id":1,
  "result":{
     "value":"c4a84b47-1acd-4930-9f6d-008c10782dfe_MediaPipeline",
     "sessionId":"ba4be2a1-2b09-444e-a368-f81825a6168c"
  },
  "jsonrpc":"2.0"
}

  1. Client sends a request to create a WebRtcEndpoint:

    {
  "id":2,
  "method":"create",
  "params":{
     "type":"WebRtcEndpoint",
     "constructorParams":{
        "mediaPipeline":"c4a84b47-1acd-4930-9f6d-008c10782dfe_MediaPipeline"
     },
     "properties": {},
     "sessionId":"ba4be2a1-2b09-444e-a368-f81825a6168c"
  },
  "jsonrpc":"2.0"
}

4. KMS creates the WebRtcEndpoint sending back the media element identifier to the client:

{
  "id":2,
  "result":{
     "value":"c4a84b47-1acd-4930-9f6d-008c10782dfe_MediaPipeline/e72a1ff5-e416-48ff-99ef-02f7fadabaf7_WebRtcEndpoint",
     "sessionId":"ba4be2a1-2b09-444e-a368-f81825a6168c"
  },
  "jsonrpc":"2.0"
}

5. Client invokes the connect primitive in the WebRtcEndpoint in order to create a loopback:

{
  "id":3,
  "method":"invoke",
  "params":{
     "object":"c4a84b47-1acd-4930-9f6d-008c10782dfe_MediaPipeline/e72a1ff5-e416-48ff-99ef-02f7fadabaf7_WebRtcEndpoint",
     "operation":"connect",
     "operationParams":{
        "sink":"c4a84b47-1acd-4930-9f6d-008c10782dfe_MediaPipeline/e72a1ff5-e416-48ff-99ef-02f7fadabaf7_WebRtcEndpoint"
     },
     "sessionId":"ba4be2a1-2b09-444e-a368-f81825a6168c"
  },
  "jsonrpc":"2.0"
}

  1. KMS carry out the connection and acknowledges the operation:

    {
  "id":3,
  "result":{
     "sessionId":"ba4be2a1-2b09-444e-a368-f81825a6168c"
  },
  "jsonrpc":"2.0"
}

7. Client invokes the processOffer primitive in the WebRtcEndpoint in order to negotiate SDP in WebRTC:

{
  "id":4,
  "method":"invoke",
  "params":{
     "object":"c4a84b47-1acd-4930-9f6d-008c10782dfe_MediaPipeline/e72a1ff5-e416-48ff-99ef-02f7fadabaf7_WebRtcEndpoint",
     "operation":"processOffer",
     "operationParams":{
        "offer":"SDP"
     },
     "sessionId":"ba4be2a1-2b09-444e-a368-f81825a6168c"
  },
  "jsonrpc":"2.0"
}

  1. KMS carry out the SDP negotiation and returns the SDP answer:

    {
  "id":4,
  "result":{
     "value":"SDP"
  },
  "jsonrpc":"2.0"
}
Kurento Module Creator

The default Kurento clients (Java and JavaScript) are created using a tool called Kurento Module Creator. Therefore, this tool can be also be used to create custom clients in other languages.

Kurento Module Creator can be installed in an Ubuntu machine using the following command:

sudo apt-get install kurento-module-creator

The aim of this tools is to generate the client code and also the glue code needed in the server-side. For code generation it uses Freemarker as template engine. The typical way to use Kurento Module Creator is by running a command like this:

kurento-module-creator -c <CODEGEN_DIR> -r <ROM_FILE> -r <TEMPLATES_DIR>

Where:

  • CODEGEN_DIR: Destination directory for generated files.
  • ROM_FILE: A space separated list of Kurento Media Element Description (kmd) files or folders containing this files. As an example, you can take a look to the kmd files within the Kurento Media Server source code.
  • TEMPLATES_DIR: Directory that contains template files. As an example, you can take a look to the internal Java and JavaScript templates.

Advanced Installation Guide

Kurento Media Server Advanced Installation guide

Kurento Media Server Configuration

The main KMS configuration file is located in /etc/kurento/kurento.conf.json. After a fresh installation this file is the following:

{
  "mediaServer" : {
    "resources": {
    //  //Resources usage limit for raising an exception when an object creation is attempted
    //  "exceptionLimit": "0.8",
    //  // Resources usage limit for restarting the server when no objects are alive
    //  "killLimit": "0.7",
        // Garbage collector period in seconds
        "garbageCollectorPeriod": 240
    },
    "net" : {
      "websocket": {
        "port": 8888,
        //"secure": {
        //  "port": 8433,
        //  "certificate": "defaultCertificate.pem",
        //  "password": ""
        //},
        //"registrar": {
        //  "address": "ws://localhost:9090",
        //  "localAddress": "localhost"
        //},
        "path": "kurento",
        "threads": 10
      }
    }
  }
}

As of Kurento Media Server version 6, in addition to this general configuration file, the specific features of KMS are tuned as individual modules. Each of these modules has its own configuration file:

  • /etc/kurento/modules/kurento/MediaElement.conf.ini: Generic parameters for Media Elements.
  • /etc/kurento/modules/kurento/SdpEndpoint.conf.ini: Audio/video parameters for SdpEndpoints (i.e. WebRtcEndpoint and RtpEndpoint).
  • /etc/kurento/modules/kurento/WebRtcEndpoint.conf.ini: Specific parameters for WebRtcEndpoint.
  • /etc/kurento/modules/kurento/HttpEndpoint.conf.ini: Specific parameters for HttpEndpoint.
Verifying Kurento Media Server installation
Kurento Media Server Process

To verify that KMS is up and running use the command:

ps -ef | grep kurento-media-server

The output should include the kurento-media-server process:

nobody    1270     1  0 08:52 ?        00:01:00 /usr/bin/kurento-media-server
WebSocket Port

Unless configured otherwise, KMS will open the port 8888 to receive requests and send responses to/from by means of the Kurento Protocol. To verify if this port is listening execute the following command:

sudo netstat -putan | grep kurento

The output should be similar to the following:

tcp6    0    0 :::8888    :::*    LISTEN    1270/kurento-media-server
Kurento Media Server Log

Kurento Media Server logs file are stored in the folder /var/log/kurento-media-server/. The content of this folder is as follows:

  • media-server_<timestamp>.<log_number>.<kms_pid>.log: Current log for Kurento Media Server.
  • media-server_error.log: Third-party errors.
  • logs: Folder that contains the KMS rotated logs.

Each line in the Kurento Media Server logs has a fixed structure, as follows:

[timestamp] [pid] [memory]   [level] [component]    [filename:loc] [method] [message]

... where:

  • [timestamp] : Date and time of the logging trace (e.g. 2016-10-26 12:04:22,493295).
  • [pid] : Process identifier of kurento-media-sever (e.g. 17521).
  • [memory] : Memory address in which the kurento-media-sever component is running (e.g. 0x00007fd59f2a78c0).
  • [level] : Log level. This value typically will be info and debug. If unexpected error situation happens, the error level will contain information about the problem.
  • [component] : Kurento Media Server component name, for example KurentoModuleManager, KurentoLoadConfig, or KurentoMediaServer, among others.
  • [filename:loc] : Code source file name (e.g. main.cp) followed by the line of code (loc) number.
  • [method] : Name of the method of function in which the log trace is invoked (e.g. loadModule(), doGarbageCollection(), etc).
  • [message] : Specific log information.

For example, when KMS starts correctly, this trace is written in the log file:

[timestamp] [pid] [memory]  info KurentoMediaServer  main.cpp:256 main()  Mediaserver started

Working with Nightly Builds

Working with nightly builds

Kurento is composed by several components. Each component is being developed with very different technologies.

  • Kurento Media Server: This is the core component of Kurento. It is implemented using C/C++ and GStreamer platform.
  • Kurento Java Client: This Kurento Client is implemented in Java with Maven and Sprint.
  • Kurento JavaScript Client: This Kurento Client is implemented in JavaScript with Node.js and NPM.

In this section, we will see how to use nightly compiled versions of Kurento code base. This is not the recommended way to use Kurento, but can be useful if you are testing brand new features.

We’ll also explain in detail how Kurento can be built from sources. This is a complex task because Kurento uses several technologies, although it can be very funny ;)

Using development versions

In this section we are going to explain how to use development versions of Kurento. We build every Kurento component at least once a day as we follow the Continuous Integration principles.

Some components are build nightly, with the code developed that day. Other components are created automatically when code is merged into source repository.

Using development versions is not the recommended way to use Kurento, but it can be useful to try brand new features.

警告

You have to use this versions with caution, because them can be broken. Usually they have bugs and incomplete functionalities. Never use development versions in production.

Kurento Media Server

To install packages from development (unstable) repository you need to execute:

echo "deb http://ubuntu.kurento.org trusty-dev kms6" | sudo tee /etc/apt/sources.list.d/kurento-dev.list
wget -O - http://ubuntu.kurento.org/kurento.gpg.key | sudo apt-key add -
sudo apt-get update
sudo apt-get install kurento-media-server-6.0
sudo apt-get dist-upgrade

As you can imagine, it is not possible to have installed at the same time latest stable version and latest development version of Kurento Media Server.

In order to install older versions of Kurento Media Server, you need to configure the proper repository (trusty or xenial) in your apt sources:

deb http://ubuntu.kurento.org/[VERSION_TAG] trusty kms6
deb http://ubuntu.kurento.org/[VERSION_TAG] xenial kms6

... where [VERSION_TAG] is the version of Kurento Media Server to be installed (for instance, 6.4.0). After that you should install KMS as usual:

sudo apt-get update
sudo apt-get install kurento-media-server-6.0

Notice that an old version of KMS cannot live in the same machine that a stable/unstable release. Therefore, if you have KMS previously installed and you want to downgrade to a former release, first your need to purge your previous installation:

sudo apt-get remove kurento-media-server-6.0
sudo apt-get purge kurento-media-server-6.0
sudo apt-get autoremove
sudo apt-get dist-upgrade
Kurento Java Client

The development builds of Kurento Java Client Maven artifacts hosted in http://maven.kurento.org.

To use development versions, first you have to add this repository in your Maven installation as a valid snapshot repository. To do this, add following configuration repository to the repositories section to file ~/.m2/settings.xml:

<repositories>
   <repository>
       <id>kurento-snapshots</id>
       <name>Kurento Snapshot Repository</name>
       <url>http://maven.kurento.org/snapshots/</url>
       <releases>
           <enabled>false</enabled>
       </releases>
       <snapshots>
           <enabled>true</enabled>
       </snapshots>
   </repository>
</repositories>
<pluginRepositories>
   <pluginRepository>
      <id>kurento-snapshots</id>
      <name>Kurento Snapshot Repository</name>
      <url>http://maven.kurento.org/snapshots/</url>
      <releases>
         <enabled>false</enabled>
      </releases>
      <snapshots>
         <enabled>true</enabled>
      </snapshots>
   </pluginRepository>
</pluginRepositories>

Then, you have to change the dependency in your application’s pom.xml to point to a development version. There is no way in Maven to use the latest development version of an artifact. You have to specify the concrete development version you want to depend on. To know what is the current Kurento Java Client development version, you can take a look to the internal Kurento Maven repository and search for the latest version. Then, you have to include in your application’s pom.xml the following dependency:

<dependency>
    <groupId>org.kurento</groupId>
    <artifactId>kurento-client</artifactId>
    <version>latest-version-SNAPSHOT</version>
</dependency>
Kurento JavaScript Client

JavaScript is special because in some cases there is no need to build anything. JavaScript is a scripting language that can execute directly from sources. But in some cases, the code have to be “processed” to be used from client applications.

Node.js development

If you are using Kurento JavaScript Client from a Node.js application and want to use the latest development version of this library, you have to change the dependencies section in the application’s package.json. You have to point directly to the development repository, that is:

"dependencies": {
    "kurento-client": "Kurento/kurento-client-js#master"
}
Browser JavaScript development

If you are using Kurento JavaScript Client from a browser application with Bower and want to use the latest development version of this library, you have to change the dependencies section in the application’s bower.json. You have to point directly to the development bower repository, that is:

"dependencies": {
    "kurento-client": "master"
    "kurento-utils": "master"
}

Alternatively, if your browser application is pointing directly to JavaScript libraries from HTML resources, then, you have to change to development URLs:

<script type="text/javascript"
    src="http://builds.kurento.org/dev/master/latest/js/kurento-client.min.js"></script>

Kurento Modules

Kurento Modules

Kurento is a pluggable framework. Each plugin in Kurento is called module. We classify Kurento modules into three groups, namely:

  • Main modules. Incorporated out of the box with Kurento Media Server

    • kms-core: Main components of Kurento Media Server.
    • kms-elements: Implementation of Kurento Media Elements (WebRtcEndpoint, PlayerEndpoint, and so on).
    • kms-filters: Implementation of Kurento Filters (FaceOverlayFilter, ZBarFilter, GStreamerFilter).

  • Built-in modules. Extra modules developed by the Kurento team to enhance the basic capabilities of Kurento Media Server. So far, there are four built-in modules, namely:

    • kms-pointerdetector: Filter that detects pointers in video streams based on color tracking. The command to install this module is:

      sudo apt-get install kms-pointerdetector-6.0

    • kms-chroma: Filter that makes transparent a color range in the top layer, revealing another image behind.

      sudo apt-get install kms-chroma-6.0

    • kms-crowddetector: Filter that detects people agglomeration in video streams.

      sudo apt-get install kms-crowddetector-6.0

    • kms-platedetector: Filter that detects vehicle plates in video streams.

      sudo apt-get install kms-platedetector-6.0

      警告

      Plate detector module is a prototype and its results is not always accurate. Consider this if you are planning to use this module in a production environment.

  • Custom modules. Extensions to Kurento Media Server which provides new media capabilities. If you are planning to develop your own custom module, please take a look to the following page:

How to Develop Kurento Modules

You can expand the Kurento Media Server developing your own modules. There are two flavors of Kurento modules:

  • Modules based on OpenCV. This kind of modules are recommended if you would like to develop a computer vision filter.
  • Modules based on GStreamer. This kind of modules are more powerful but also they are more difficult to develop. Skills in GStreamer development are necessary.

The starting point to develop a filter is create the filter structure. For this task, you can use the kurento-module-scaffold tool. This tool is distributed with the kurento-media-server-6.0-dev package. To install this tool run this command in the shell:

sudo apt-get install kurento-media-server-6.0-dev

The tool usage is different depending on the chosen flavor:

  1. OpenCV module:
kurento-module-scaffold.sh <module_name> <output_directory> opencv_filter
  1. Gstreamer module:
kurento-module-scaffold.sh <module_name> <output_directory>

The tool generates the folder tree, all the CmakeLists.txt files necessaries and example files of Kurento module descriptor files (.kmd). These files describe our modules, the constructor, the methods, the properties, the events and the complex types defined by the developer.

Once, kmd files are completed we can generate code. The tool kurento-module-creator generates glue code to server-side. From the root directory:

cd build
cmake ..

The following section details how to create your module depending on the filter type you chose (OpenCV or GStreamer):

OpenCV module

We have four files in src/server/implementation:

ModuleNameImpl.cpp
ModuleNameImpl.hpp
ModuleNameOpenCVImpl.cpp
ModuleNameOpenCVImpl.hpp

The first two files should not be modified. The last two files will contain the logic of your module. The file ModuleNameOpenCVImpl.cpp contains functions to deal with the methods and the parameters (you must implement the logic). Also, this file contains a function called process. This function will be called with each new frame, thus you must implement the logic of your filter inside this function.

GStreamer module

In this case, we have two directories inside the src folder. The gst-plugins folder contains the implementation of your GStreamer element (the kurento-module-scaffold generates a dummy filter). Inside the server/objects folder you have two files:

ModuleNameImpl.cpp
ModuleNameImpl.hpp

In the file ModuleNameImpl.cpp you have to invoke the methods of your GStreamer element. The module logic will be implemented in the GStreamer element.

For both kind of modules

If you need extra compilation dependencies you can add compilation rules to the kurento-module-creator using the function generate_code in the CmakeLists.txt file in src/server. The following parameters are available:

  • MODELS (required): This parameter receives the folders where the models (.kmd files) are located.

  • INTERFACE_LIB_EXTRA_SOURCES, INTERFACE_LIB_EXTRA_HEADERS, INTERFACE_LIB_EXTRA_INCLUDE_DIRS, INTERFACE_LIB_EXTRA_LIBRARIES: These parameters allow to add additional source code to the static library. Files included in INTERFACE_LIB_EXTRA_HEADERS will be installed in the system as headers for this library. All the parameters accept a list as input.

  • SERVER_IMPL_LIB_EXTRA_SOURCES, SERVER_IMPL_LIB_EXTRA_HEADERS, SERVER_IMPL_LIB_EXTRA_INCLUDE_DIRS, SERVER_IMPL_LIB_EXTRA_LIBRARIES: These parameters allows to add additional source code to the interface library. Files included in SERVER_IMPL_LIB_EXTRA_HEADERS will be installed in the system as headers for this library. All the parameters accept a list as input.

  • MODULE_EXTRA_INCLUDE_DIRS, MODULE_EXTRA_LIBRARIES: These parameters allows to add extra include directories and libraries to the module.

  • SERVER_IMPL_LIB_FIND_CMAKE_EXTRA_LIBRARIES: This parameter receives a list of strings, each string has this format libname[ libversion range] (possible ranges can use symbols AND OR < <= > >= ^ and ~):

    ^ indicates a version compatible using Semantic Versioning

    ~ Indicates a version similar, that can change just last indicated version character

  • SERVER_STUB_DESTINATION (required): The generated code that you may need to modify will be generated on the folder indicated by this parameter.

Once the module logic is implemented and the compilation process is finished, you need to install your module in your system. You can follow two different ways:

You can generate the Debian package (debuild -us -uc) and install it (dpkg -i) or you can define the following environment variables in the file /etc/default/kurento: KURENTO_MODULES_PATH=<module_path>/build/src GST_PLUGIN_PATH=<module_path>/build/src.

Now, you need to generate code for Java or JavaScript to use your module from the client-side.

  • For Java, from the build directory you have to execute cmake .. -DGENERATE_JAVA_CLIENT_PROJECT=TRUE command generates a Java folder with client code. You can run make java_install and your module will be installed in your Maven local repository. To use the module in your Maven project, you have to add the dependency to the pom.xml file:
<dependency>
   <groupId>org.kurento.module</groupId>
   <artifactId>modulename</artifactId>
   <version>moduleversion</version>
</dependency>
  • For JavaScript, you should to execute cmake .. -DGENERATE_JS_CLIENT_PROJECT=TRUE. This command generates a js folder with client code. Now you can add the JavaScript library to use your module in your application manually. Alternatively, you can use Bower (for JavaScript for browser) or NPM (for JavaScript for Node.js). To do that, you should add your JavaScript module as a dependency in your bower.json or package.json file respectively, as follows:
"dependencies": {
   "modulename": "moduleversion"
}
Examples

Simple examples for both kind of modules are available in GitHub:

There are a lot of examples of how to define methods, parameters or events in all our public built-in modules:

Moreover, all our modules are developed using this methodology, for that reason you can take a look to our main modules:

The following picture shows an schematic view of the Kurento Media Server as described before:

Kurento modules architecture

Kurento modules architecture. Kurento Media Server can be extended with built-it modules (crowddetector, pointerdetector, chroma, platedetector) and also with other custom modules.

Taking into account the built-in modules, the Kurento toolbox is extended as follows:

Extended Kurento Toolbox

Extended Kurento Toolbox. The basic Kurento toolbox (left side of the picture) is extended with more computer vision and augmented reality filters (right side of the picture) provided by the built-in modules.

The remainder of this page is structured in four sections in which the built-in modules (kms-pointerdetector, kms-chroma, kms-crowddetector, kms-platedetector) are used to develop simple applications (tutorials) aimed to show how to use them.

Module Tutorial - Pointer Detector Filter

This web application consists on a WebRTC video communication in mirror (loopback) with a pointer tracking filter element.

Java Module - Pointer Detector Filter

This web application consists on a WebRTC video communication in mirror (loopback) with a pointer tracking filter element.

注解

This tutorial has been configured to use https. Follow the instructions to secure your application.

For the impatient: running this example

First of all, you should install Kurento Media Server to run this demo. Please visit the installation guide for further information. In addition, the built-in module kms-pointerdetector-6.0 should be also installed:

sudo apt-get install kms-pointerdetector-6.0

To launch the application, you need to clone the GitHub project where this demo is hosted, and then run the main class:

git clone https://github.com/Kurento/kurento-tutorial-java.git
cd kurento-tutorial-java/kurento-pointerdetector
git checkout 6.6.2
mvn compile exec:java

The web application starts on port 8443 in the localhost by default. Therefore, open the URL https://localhost:8443/ in a WebRTC compliant browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the flag kms.url to the JVM executing the demo. As we’ll be using maven, you should execute the following command

mvn compile exec:java -Dkms.url=ws://kms_host:kms_port/kurento
Understanding this example

This application uses computer vision and augmented reality techniques to detect a pointer in a WebRTC stream based on color tracking.

The interface of the application (an HTML web page) is composed by two HTML5 video tags: one for the video camera stream (the local client-side stream) and other for the mirror (the remote stream). The video camera stream is sent to Kurento Media Server, which processes and sends it back to the client as a remote stream. To implement this, we need to create a Media Pipeline composed by the following Media Element s:

WebRTC with PointerDetector filter in loopback Media Pipeline

WebRTC with PointerDetector filter in loopback Media Pipeline

The complete source code of this demo can be found in GitHub.

This example is a modified version of the Magic Mirror tutorial. In this case, this demo uses a PointerDetector instead of FaceOverlay filter.

In order to perform pointer detection, there must be a calibration stage, in which the color of the pointer is registered by the filter. To accomplish this step, the pointer should be placed in a square visible in the upper left corner of the video after going thorugh the filter, as follows:

Pointer calibration stage

Pointer calibration stage

When the desired color to track is filling that box, a calibration message is sent from the client to the server. This is done by clicking on the Calibrate blue button of the GUI.

After that, the color of the pointer is tracked in real time by Kurento Media Server. PointerDetectorFilter can also define regions in the screen called windows in which some actions are performed when the pointer is detected when the pointer enters (WindowInEvent event) and exits (WindowOutEvent event) the windows. This is implemented in the server-side logic as follows:

// Media Logic (Media Pipeline and Elements)
UserSession user = new UserSession();
MediaPipeline pipeline = kurento.createMediaPipeline();
user.setMediaPipeline(pipeline);
WebRtcEndpoint webRtcEndpoint = new WebRtcEndpoint.Builder(pipeline)
      .build();
user.setWebRtcEndpoint(webRtcEndpoint);
users.put(session.getId(), user);

webRtcEndpoint
      .addIceCandidateFoundListener(new EventListener<IceCandidateFoundEvent>() {

   @Override
   public void onEvent(IceCandidateFoundEvent event) {
      JsonObject response = new JsonObject();
      response.addProperty("id", "iceCandidate");
      response.add("candidate", JsonUtils
      .toJsonObject(event.getCandidate()));
      try {
         synchronized (session) {
      session.sendMessage(new TextMessage(
            response.toString()));
         }
      } catch (IOException e) {
         log.debug(e.getMessage());
      }
   }
      });

pointerDetectorFilter = new PointerDetectorFilter.Builder(pipeline,
      new WindowParam(5, 5, 30, 30)).build();

pointerDetectorFilter
      .addWindow(new PointerDetectorWindowMediaParam("window0",
      50, 50, 500, 150));

pointerDetectorFilter
      .addWindow(new PointerDetectorWindowMediaParam("window1",
      50, 50, 500, 250));

webRtcEndpoint.connect(pointerDetectorFilter);
pointerDetectorFilter.connect(webRtcEndpoint);

pointerDetectorFilter
      .addWindowInListener(new EventListener<WindowInEvent>() {
   @Override
   public void onEvent(WindowInEvent event) {
      JsonObject response = new JsonObject();
      response.addProperty("id", "windowIn");
      response.addProperty("roiId", event.getWindowId());
      try {
         session.sendMessage(new TextMessage(response
         .toString()));
      } catch (Throwable t) {
         sendError(session, t.getMessage());
      }
   }
      });

pointerDetectorFilter
      .addWindowOutListener(new EventListener<WindowOutEvent>() {

   @Override
   public void onEvent(WindowOutEvent event) {
      JsonObject response = new JsonObject();
      response.addProperty("id", "windowOut");
      response.addProperty("roiId", event.getWindowId());
      try {
         session.sendMessage(new TextMessage(response
         .toString()));
      } catch (Throwable t) {
         sendError(session, t.getMessage());
      }
   }
      });

// SDP negotiation (offer and answer)
String sdpOffer = jsonMessage.get("sdpOffer").getAsString();
String sdpAnswer = webRtcEndpoint.processOffer(sdpOffer);

// Sending response back to client
JsonObject response = new JsonObject();
response.addProperty("id", "startResponse");
response.addProperty("sdpAnswer", sdpAnswer);
synchronized (session) {
   session.sendMessage(new TextMessage(response.toString()));
}

webRtcEndpoint.gatherCandidates();

The following picture illustrates the pointer tracking in one of the defined windows:

Pointer tracking over a window

Pointer tracking over a window

In order to send the calibration message from the client side, this function is used in the JavaScript side of this demo:

function calibrate() {
   console.log("Calibrate color");

   var message = {
         id : 'calibrate'
      }
   sendMessage(message);
}

When this message is received in the application server side, this code is execute to carry out the calibration:

private void calibrate(WebSocketSession session, JsonObject jsonMessage) {
   if (pointerDetectorFilter != null) {
      pointerDetectorFilter.trackColorFromCalibrationRegion();
   }
}
Dependencies

This Java Spring application is implemented using Maven. The relevant part of the pom.xml is where Kurento dependencies are declared. As the following snippet shows, we need two dependencies: the Kurento Client Java dependency (kurento-client) and the JavaScript Kurento utility library (kurento-utils) for the client-side. Other client libraries are managed with webjars:

<dependencies>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-client</artifactId>
   </dependency>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-utils-js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars</groupId>
      <artifactId>webjars-locator</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>bootstrap</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>demo-console</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>adapter.js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>jquery</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>ekko-lightbox</artifactId>
   </dependency>
</dependencies>

注解

We are in active development. You can find the latest version of Kurento Java Client at Maven Central.

Kurento Java Client has a minimum requirement of Java 7. Hence, you need to include the following properties in your pom:

<maven.compiler.target>1.7</maven.compiler.target>
<maven.compiler.source>1.7</maven.compiler.source>
JavaScript Module - Pointer Detector Filter

This web application consists on a WebRTC video communication in mirror (loopback) with a pointer tracking filter element.

注解

This tutorial has been configurated for using https. Follow these instructions for securing your application.

For the impatient: running this example

First of all, you should install Kurento Media Server to run this demo. Please visit the installation guide for further information. In addition, the built-in module kms-pointerdetector-6.0 should be also installed:

sudo apt-get install kms-pointerdetector-6.0

Be sure to have installed Node.js and Bower in your system. In an Ubuntu machine, you can install both as follows:

curl -sL https://deb.nodesource.com/setup_4.x | sudo bash -
sudo apt-get install -y nodejs
sudo npm install -g bower

Due to Same-origin policy, this demo has to be served by an HTTP server. A very simple way of doing this is by means of an HTTP Node.js server which can be installed using npm :

sudo npm install http-server -g

You also need the source code of this demo. You can clone it from GitHub. Then start the HTTP server:

git clone https://github.com/Kurento/kurento-tutorial-js.git
cd kurento-tutorial-js/kurento-pointerdetector
git checkout 6.6.1
bower install
http-server -p 8443 -S -C keys/server.crt -K keys/server.key

Finally, access the application connecting to the URL https://localhost:8443/ through a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. Kurento Media Server must use WebSockets over SSL/TLS (WSS), so make sure you check this too. It is possible to locate the KMS in other machine simple adding the parameter ws_uri to the URL:

https://localhost:8443/index.html?ws_uri=wss://kms_host:kms_port/kurento

Notice that the Kurento Media Server must connected using a Secure WebSocket (i.e., the KMS URI starts with wss://). For this reason, the support for secure WebSocket must be enabled in the Kurento Media Server you are using to run this tutorial. For further information about securing applications, please visit the following page.

Understanding this example

This application uses computer vision and augmented reality techniques to detect a pointer in a WebRTC stream based on color tracking.

The interface of the application (an HTML web page) is composed by two HTML5 video tags: one for the video camera stream (the local client-side stream) and other for the mirror (the remote stream). The video camera stream is sent to Kurento Media Server, which processes and sends it back to the client as a remote stream. To implement this, we need to create a Media Pipeline composed by the following Media Element s:

WebRTC with PointerDetector filter in loopback Media Pipeline

WebRTC with PointerDetector filter in loopback Media Pipeline

The complete source code of this demo can be found in GitHub.

This example is a modified version of the Magic Mirror tutorial. In this case, this demo uses a PointerDetector instead of FaceOverlay filter.

In order to perform pointer detection, there must be a calibration stage, in which the color of the pointer is registered by the filter. To accomplish this step, the pointer should be placed in a square in the upper left corner of the video, as follows:

Pointer calibration stage

Pointer calibration stage

注解

Modules can have options. For configuring these options, you’ll need to get the constructor for them. In Javascript and Node, you have to use kurentoClient.getComplexType(‘qualifiedName’) . There is an example in the code.

In that precise moment, a calibration operation should be carried out. This is done by clicking on the Calibrate blue button of the GUI.

After that, the color of the pointer is tracked in real time by Kurento Media Server. PointerDetectorFilter can also define regions in the screen called windows in which some actions are performed when the pointer is detected when the pointer enters (WindowIn event) and exits (WindowOut event) the windows. This is implemented in the JavaScript logic as follows:

...
kurentoClient.register('kurento-module-pointerdetector')
const PointerDetectorWindowMediaParam = kurentoClient.getComplexType('pointerdetector.PointerDetectorWindowMediaParam')
const WindowParam                     = kurentoClient.getComplexType('pointerdetector.WindowParam')
...

kurentoClient(args.ws_uri, function(error, client) {
  if (error) return onError(error);

  client.create('MediaPipeline', function(error, _pipeline) {
    if (error) return onError(error);

    pipeline = _pipeline;

    console.log("Got MediaPipeline");

    pipeline.create('WebRtcEndpoint', function(error, webRtc) {
      if (error) return onError(error);

      console.log("Got WebRtcEndpoint");

      setIceCandidateCallbacks(webRtcPeer, webRtc, onError)

      webRtc.processOffer(sdpOffer, function(error, sdpAnswer) {
        if (error) return onError(error);

        console.log("SDP answer obtained. Processing ...");

        webRtc.gatherCandidates(onError);
        webRtcPeer.processAnswer(sdpAnswer);
      });

      var options =
      {
        calibrationRegion: WindowParam({
          topRightCornerX: 5,
          topRightCornerY:5,
          width:30,
          height: 30
        })
      };

      pipeline.create('pointerdetector.PointerDetectorFilter', options, function(error, _filter) {
        if (error) return onError(error);

        filter = _filter;

        var options = PointerDetectorWindowMediaParam({
          id: 'window0',
          height: 50,
          width:50,
          upperRightX: 500,
          upperRightY: 150
        });

        filter.addWindow(options, onError);

        var options = PointerDetectorWindowMediaParam({
          id: 'window1',
          height: 50,
          width:50,
          upperRightX: 500,
          upperRightY: 250
        });

        filter.addWindow(options, onError);

        filter.on ('WindowIn', function (data){
          console.log ("Event window in detected in window " + data.windowId);
        });

        filter.on ('WindowOut', function (data){
          console.log ("Event window out detected in window " + data.windowId);
        });

        console.log("Connecting ...");
        client.connect(webRtc, filter, webRtc, function(error) {
          if (error) return onError(error);

          console.log("WebRtcEndpoint --> Filter --> WebRtcEndpoint");
        });
      });
    });
  });
});

The following picture illustrates the pointer tracking in one of the defined windows:

Pointer tracking over a window

Pointer tracking over a window

In order to carry out the calibration process, this JavaScript function is used:

function calibrate() {
  if(filter) filter.trackColorFromCalibrationRegion(onError);
}

function onError(error) {
  if(error) console.error(error);
}

注解

The TURN and STUN servers to be used can be configured simple adding the parameter ice_servers to the application URL, as follows:

https://localhost:8443/index.html?ice_servers=[{"urls":"stun:stun1.example.net"},{"urls":"stun:stun2.example.net"}]
https://localhost:8443/index.html?ice_servers=[{"urls":"turn:turn.example.org","username":"user","credential":"myPassword"}]
Dependencies

The dependencies of this demo has to be obtained using Bower. The definition of these dependencies are defined in the bower.json file, as follows:

"dependencies": {
   "kurento-client": "6.6.0",
   "kurento-utils": "6.6.2"
   "kurento-module-pointerdetector": "6.6.0"
}

To get these dependencies, just run the following shell command:

bower install

注解

We are in active development. You can find the latest versions at Bower.

Node.js Module - Pointer Detector Filter

This web application consists on a WebRTC video communication in mirror (loopback) with a pointer tracking filter element.

注解

This tutorial has been configurated for using https. Follow these instructions for securing your application.

For the impatient: running this example

First of all, you should install Kurento Media Server to run this demo. Please visit the installation guide for further information. In addition, the built-in module kms-pointerdetector-6.0 should be also installed:

sudo apt-get install kms-pointerdetector-6.0

Be sure to have installed Node.js and Bower in your system. In an Ubuntu machine, you can install both as follows:

curl -sL https://deb.nodesource.com/setup_4.x | sudo bash -
sudo apt-get install -y nodejs
sudo npm install -g bower

To launch the application, you need to clone the GitHub project where this demo is hosted, install it and run it:

git clone https://github.com/Kurento/kurento-tutorial-node.git
cd kurento-tutorial-node/kurento-pointerdetector
git checkout 6.6.1
npm install

If you have problems installing any of the dependencies, please remove them and clean the npm cache, and try to install them again:

rm -r node_modules
npm cache clean

Finally, access the application connecting to the URL https://localhost:8443/ through a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the argument ws_uri to the npm execution command, as follows:

npm start -- --ws_uri=ws://kms_host:kms_port/kurento

In this case you need to use npm version 2. To update it you can use this command:

sudo npm install npm -g
Understanding this example

This application uses computer vision and augmented reality techniques to detect a pointer in a WebRTC stream based on color tracking.

The interface of the application (an HTML web page) is composed by two HTML5 video tags: one for the video camera stream (the local client-side stream) and other for the mirror (the remote stream). The video camera stream is sent to Kurento Media Server, which processes and sends it back to the client as a remote stream. To implement this, we need to create a Media Pipeline composed by the following Media Element s:

WebRTC with PointerDetector filter in loopback Media Pipeline

WebRTC with PointerDetector filter in loopback Media Pipeline

The complete source code of this demo can be found in GitHub.

This example is a modified version of the Magic Mirror tutorial. In this case, this demo uses a PointerDetector instead of FaceOverlay filter.

In order to perform pointer detection, there must be a calibration stage, in which the color of the pointer is registered by the filter. To accomplish this step, the pointer should be placed in a square in the upper left corner of the video, as follows:

Pointer calibration stage

Pointer calibration stage

注解

Modules can have options. For configuring these options, you’ll need to get the constructor for them. In Javascript and Node, you have to use kurentoClient.getComplexType(‘qualifiedName’) . There is an example in the code.

In that precise moment, a calibration operation should be carried out. This is done by clicking on the Calibrate blue button of the GUI.

After that, the color of the pointer is tracked in real time by Kurento Media Server. PointerDetectorFilter can also define regions in the screen called windows in which some actions are performed when the pointer is detected when the pointer enters (WindowIn event) and exits (WindowOut event) the windows. This is implemented in the JavaScript logic as follows:

...
kurento.register('kurento-module-pointerdetector');
const PointerDetectorWindowMediaParam = kurento.getComplexType('pointerdetector.PointerDetectorWindowMediaParam');
const WindowParam                     = kurento.getComplexType('pointerdetector.WindowParam');
...

function start(sessionId, ws, sdpOffer, callback) {
    if (!sessionId) {
        return callback('Cannot use undefined sessionId');
    }

    getKurentoClient(function(error, kurentoClient) {
        if (error) {
            return callback(error);
        }

        kurentoClient.create('MediaPipeline', function(error, pipeline) {
            if (error) {
                return callback(error);
            }

            createMediaElements(pipeline, ws, function(error, webRtcEndpoint, filter) {
                if (error) {
                    pipeline.release();
                    return callback(error);
                }

                if (candidatesQueue[sessionId]) {
                    while(candidatesQueue[sessionId].length) {
                        var candidate = candidatesQueue[sessionId].shift();
                        webRtcEndpoint.addIceCandidate(candidate);
                    }
                }

                connectMediaElements(webRtcEndpoint, filter, function(error) {
                    if (error) {
                        pipeline.release();
                        return callback(error);
                    }

                    webRtcEndpoint.on('OnIceCandidate', function(event) {
                        var candidate = kurento.getComplexType('IceCandidate')(event.candidate);
                        ws.send(JSON.stringify({
                            id : 'iceCandidate',
                            candidate : candidate
                        }));
                    });

                    filter.on('WindowIn', function (_data) {
                        return callback(null, 'WindowIn', _data);
                    });

                    filter.on('WindowOut', function (_data) {
                        return callback(null, 'WindowOut', _data);
                    });

                    var options1 = PointerDetectorWindowMediaParam({
                        id: 'window0',
                        height: 50,
                        width: 50,
                        upperRightX: 500,
                        upperRightY: 150
                    });
                    filter.addWindow(options1, function(error) {
                        if (error) {
                            pipeline.release();
                            return callback(error);
                        }
                    });

                    var options2 = PointerDetectorWindowMediaParam({
                        id: 'window1',
                        height: 50,
                        width:50,
                        upperRightX: 500,
                        upperRightY: 250
                    });
                    filter.addWindow(options2, function(error) {
                        if (error) {
                            pipeline.release();
                            return callback(error);
                        }
                    });

                    webRtcEndpoint.processOffer(sdpOffer, function(error, sdpAnswer) {
                        if (error) {
                            pipeline.release();
                            return callback(error);
                        }

                        sessions[sessionId] = {
                            'pipeline' : pipeline,
                            'webRtcEndpoint' : webRtcEndpoint,
                            'pointerDetector' : filter
                        }
                        return callback(null, 'sdpAnswer', sdpAnswer);
                    });

                    webRtcEndpoint.gatherCandidates(function(error) {
                        if (error) {
                            return callback(error);
                        }
                    });
                });
            });
        });
    });
}

function createMediaElements(pipeline, ws, callback) {
    pipeline.create('WebRtcEndpoint', function(error, webRtcEndpoint) {
        if (error) {
            return callback(error);
        }

        var options = {
            calibrationRegion: WindowParam({
                topRightCornerX: 5,
                topRightCornerY:5,
                width:30,
                height: 30
            })
        };

        pipeline.create('pointerdetector.PointerDetectorFilter', options, function(error, filter) {
            if (error) {
                return callback(error);
            }

            return callback(null, webRtcEndpoint, filter);
        });
    });
}

The following picture illustrates the pointer tracking in one of the defined windows:

Pointer tracking over a window

Pointer tracking over a window

In order to carry out the calibration process, this JavaScript function is used:

function calibrate() {
   if (webRtcPeer) {
      console.log("Calibrating...");
      var message = {
         id : 'calibrate'
      }
      sendMessage(message);
   }
}
Dependencies

Dependencies of this demo are managed using NPM. Our main dependency is the Kurento Client JavaScript (kurento-client). The relevant part of the package.json file for managing this dependency is:

"dependencies": {
   "kurento-client" : "6.6.0"
}

At the client side, dependencies are managed using Bower. Take a look to the bower.json file and pay attention to the following section:

"dependencies": {
   "kurento-utils" : "6.6.2",
   "kurento-module-pointerdetector": "6.6.0"
}

注解

We are in active development. You can find the latest versions at npm and Bower.

Module Tutorial - Chroma Filter

This web application consists on a WebRTC video communication in mirror (loopback) with a chroma filter element.

Java Module - Chroma Filter

This web application consists on a WebRTC video communication in mirror (loopback) with a chroma filter element.

注解

This tutorial has been configured to use https. Follow the instructions to secure your application.

For the impatient: running this example

First of all, you should install Kurento Media Server to run this demo. Please visit the installation guide for further information. In addition, the built-in module kms-chroma-6.0 should be also installed:

sudo apt-get install kms-chroma-6.0

To launch the application, you need to clone the GitHub project where this demo is hosted, and then run the main class:

git clone https://github.com/Kurento/kurento-tutorial-java.git
cd kurento-tutorial-java/kurento-chroma
git checkout 6.6.2
mvn compile exec:java

The web application starts on port 8443 in the localhost by default. Therefore, open the URL https://localhost:8443/ in a WebRTC compliant browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the flag kms.url to the JVM executing the demo. As we’ll be using maven, you should execute the following command

mvn compile exec:java -Dkms.url=ws://kms_host:kms_port/kurento
Understanding this example

This application uses computer vision and augmented reality techniques to detect a chroma in a WebRTC stream based on color tracking.

The interface of the application (an HTML web page) is composed by two HTML5 video tags: one for the video camera stream (the local client-side stream) and other for the mirror (the remote stream). The video camera stream is sent to Kurento Media Server, which processes and sends it back to the client as a remote stream. To implement this, we need to create a Media Pipeline composed by the following Media Element s:

WebRTC with Chroma filter Media Pipeline

WebRTC with Chroma filter Media Pipeline

The complete source code of this demo can be found in GitHub.

This example is a modified version of the Magic Mirror tutorial. In this case, this demo uses a Chroma instead of FaceOverlay filter.

In order to perform chroma detection, there must be a color calibration stage. To accomplish this step, at the beginning of the demo, a little square appears in upper left of the video, as follows:

Chroma calibration stage

Chroma calibration stage

In the first second of the demo, a calibration process is done, by detecting the color inside that square. When the calibration is finished, the square disappears and the chroma is substituted with the configured image. Take into account that this process requires good lighting condition. Otherwise the chroma substitution will not be perfect. This behavior can be seen in the upper right corner of the following screenshot:

Chroma filter in action

Chroma filter in action

The media pipeline of this demo is is implemented in the server-side logic as follows:

private void start(final WebSocketSession session, JsonObject jsonMessage) {
   try {
      // Media Logic (Media Pipeline and Elements)
      UserSession user = new UserSession();
      MediaPipeline pipeline = kurento.createMediaPipeline();
      user.setMediaPipeline(pipeline);
      WebRtcEndpoint webRtcEndpoint = new WebRtcEndpoint.Builder(pipeline)
            .build();
      user.setWebRtcEndpoint(webRtcEndpoint);
      users.put(session.getId(), user);

      webRtcEndpoint
            .addIceCandidateFoundListener(new EventListener<IceCandidateFoundEvent>() {

               @Override
               public void onEvent(IceCandidateFoundEvent event) {
                  JsonObject response = new JsonObject();
                  response.addProperty("id", "iceCandidate");
                  response.add("candidate", JsonUtils
                        .toJsonObject(event.getCandidate()));
                  try {
                     synchronized (session) {
                        session.sendMessage(new TextMessage(
                              response.toString()));
                     }
                  } catch (IOException e) {
                     log.debug(e.getMessage());
                  }
               }
            });

      ChromaFilter chromaFilter = new ChromaFilter.Builder(pipeline,
            new WindowParam(5, 5, 40, 40)).build();
      String appServerUrl = System.getProperty("app.server.url",
            ChromaApp.DEFAULT_APP_SERVER_URL);
      chromaFilter.setBackground(appServerUrl + "/img/mario.jpg");

      webRtcEndpoint.connect(chromaFilter);
      chromaFilter.connect(webRtcEndpoint);

      // SDP negotiation (offer and answer)
      String sdpOffer = jsonMessage.get("sdpOffer").getAsString();
      String sdpAnswer = webRtcEndpoint.processOffer(sdpOffer);

      // Sending response back to client
      JsonObject response = new JsonObject();
      response.addProperty("id", "startResponse");
      response.addProperty("sdpAnswer", sdpAnswer);

      synchronized (session) {
         session.sendMessage(new TextMessage(response.toString()));
      }
      webRtcEndpoint.gatherCandidates();

   } catch (Throwable t) {
      sendError(session, t.getMessage());
   }
}
Dependencies

This Java Spring application is implemented using Maven. The relevant part of the pom.xml is where Kurento dependencies are declared. As the following snippet shows, we need two dependencies: the Kurento Client Java dependency (kurento-client) and the JavaScript Kurento utility library (kurento-utils) for the client-side. Other client libraries are managed with webjars:

<dependencies>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-client</artifactId>
   </dependency>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-utils-js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars</groupId>
      <artifactId>webjars-locator</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>bootstrap</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>demo-console</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>adapter.js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>jquery</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>ekko-lightbox</artifactId>
   </dependency>
</dependencies>

注解

We are in active development. You can find the latest version of Kurento Java Client at Maven Central.

Kurento Java Client has a minimum requirement of Java 7. Hence, you need to include the following properties in your pom:

<maven.compiler.target>1.7</maven.compiler.target>
<maven.compiler.source>1.7</maven.compiler.source>
JavaScript Module - Chroma Filter

This web application consists on a WebRTC video communication in mirror (loopback) with a chroma filter element.

注解

This tutorial has been configurated for using https. Follow these instructions for securing your application.

For the impatient: running this example

First of all, you should install Kurento Media Server to run this demo. Please visit the installation guide for further information. In addition, the built-in module kms-chroma-6.0 should be also installed:

sudo apt-get install kms-chroma-6.0

Be sure to have installed Node.js and Bower in your system. In an Ubuntu machine, you can install both as follows:

curl -sL https://deb.nodesource.com/setup_4.x | sudo bash -
sudo apt-get install -y nodejs
sudo npm install -g bower

Due to Same-origin policy, this demo has to be served by an HTTP server. A very simple way of doing this is by means of an HTTP Node.js server which can be installed using npm :

sudo npm install http-server -g

You also need the source code of this demo. You can clone it from GitHub. Then start the HTTP server:

git clone https://github.com/Kurento/kurento-tutorial-js.git
cd kurento-tutorial-js/kurento-chroma
git checkout 6.6.1
bower install
http-server -p 8443 -S -C keys/server.crt -K keys/server.key

Finally, access the application connecting to the URL https://localhost:8443/ through a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. Kurento Media Server must use WebSockets over SSL/TLS (WSS), so make sure you check this too. It is possible to locate the KMS in other machine simple adding the parameter ws_uri to the URL:

https://localhost:8443/index.html?ws_uri=wss://kms_host:kms_port/kurento

Notice that the Kurento Media Server must connected using a Secure WebSocket (i.e., the KMS URI starts with wss://). For this reason, the support for secure WebSocket must be enabled in the Kurento Media Server you are using to run this tutorial. For further information about securing applications, please visit the following page.

Understanding this example

This application uses computer vision and augmented reality techniques to detect a chroma in a WebRTC stream based on color tracking.

The interface of the application (an HTML web page) is composed by two HTML5 video tags: one for the video camera stream (the local client-side stream) and other for the mirror (the remote stream). The video camera stream is sent to Kurento Media Server, which processes and sends it back to the client as a remote stream. To implement this, we need to create a Media Pipeline composed by the following Media Element s:

WebRTC with Chroma filter Media Pipeline

WebRTC with Chroma filter Media Pipeline

The complete source code of this demo can be found in GitHub.

This example is a modified version of the Magic Mirror tutorial. In this case, this demo uses a Chroma instead of FaceOverlay filter.

In order to perform chroma detection, there must be a color calibration stage. To accomplish this step, at the beginning of the demo, a little square appears in upper left of the video, as follows:

Chroma calibration stage

Chroma calibration stage

In the first second of the demo, a calibration process is done, by detecting the color inside that square. When the calibration is finished, the square disappears and the chroma is substituted with the configured image. Take into account that this process requires lighting condition. Otherwise the chroma substitution will not be perfect. This behavior can be seen in the upper right corner of the following screenshot:

Chroma filter in action

Chroma filter in action

注解

Modules can have options. For configure these options, you need get the constructor to them. In Javascript and Node, you have to use kurentoClient.getComplexType(‘qualifiedName’) . There is an example in the code.

The media pipeline of this demo is is implemented in the JavaScript logic as follows:

...
kurentoClient.register('kurento-module-chroma')
const WindowParam = kurentoClient.getComplexType('chroma.WindowParam')
...

kurentoClient(args.ws_uri, function(error, client) {
  if (error) return onError(error);

  client.create('MediaPipeline', function(error, _pipeline) {
    if (error) return onError(error);

    pipeline = _pipeline;

    console.log("Got MediaPipeline");

    pipeline.create('WebRtcEndpoint', function(error, webRtc) {
      if (error) return onError(error);

      setIceCandidateCallbacks(webRtcPeer, webRtc, onError)

      webRtc.processOffer(sdpOffer, function(error, sdpAnswer) {
        if (error) return onError(error);

        console.log("SDP answer obtained. Processing...");

        webRtc.gatherCandidates(onError);
        webRtcPeer.processAnswer(sdpAnswer);
      });

      console.log("Got WebRtcEndpoint");

      var options =
      {
        window: WindowParam({
          topRightCornerX: 5,
          topRightCornerY: 5,
          width: 30,
          height: 30
        })
      }

      pipeline.create('chroma.ChromaFilter', options, function(error, filter) {
        if (error) return onError(error);

        console.log("Got Filter");

        filter.setBackground(args.bg_uri, function(error) {
          if (error) return onError(error);

          console.log("Set Image");
        });

        client.connect(webRtc, filter, webRtc, function(error) {
          if (error) return onError(error);

          console.log("WebRtcEndpoint --> filter --> WebRtcEndpoint");
        });
      });
    });
  });
});

注解

The TURN and STUN servers to be used can be configured simple adding the parameter ice_servers to the application URL, as follows:

https://localhost:8443/index.html?ice_servers=[{"urls":"stun:stun1.example.net"},{"urls":"stun:stun2.example.net"}]
https://localhost:8443/index.html?ice_servers=[{"urls":"turn:turn.example.org","username":"user","credential":"myPassword"}]
Dependencies

The dependencies of this demo has to be obtained using Bower. The definition of these dependencies are defined in the bower.json file, as follows:

"dependencies": {
   "kurento-client": "6.6.0",
   "kurento-utils": "6.6.2"
   "kurento-module-pointerdetector": "6.6.0"
}

To get these dependencies, just run the following shell command:

bower install

注解

We are in active development. You can find the latest versions at Bower.

Node.js Module - Chroma Filter

This web application consists on a WebRTC video communication in mirror (loopback) with a chroma filter element.

注解

This tutorial has been configurated for using https. Follow these instructions for securing your application.

For the impatient: running this example

First of all, you should install Kurento Media Server to run this demo. Please visit the installation guide for further information. In addition, the built-in module kms-chroma-6.0 should be also installed:

sudo apt-get install kms-chroma-6.0

Be sure to have installed Node.js and Bower in your system. In an Ubuntu machine, you can install both as follows:

curl -sL https://deb.nodesource.com/setup_4.x | sudo bash -
sudo apt-get install -y nodejs
sudo npm install -g bower

To launch the application, you need to clone the GitHub project where this demo is hosted, install it and run it:

git clone https://github.com/Kurento/kurento-tutorial-node.git
cd kurento-tutorial-node/kurento-chroma
git checkout 6.6.1
npm install

If you have problems installing any of the dependencies, please remove them and clean the npm cache, and try to install them again:

rm -r node_modules
npm cache clean

Finally, access the application connecting to the URL https://localhost:8443/ through a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the argument ws_uri to the npm execution command, as follows:

npm start -- --ws_uri=ws://kms_host:kms_port/kurento

In this case you need to use npm version 2. To update it you can use this command:

sudo npm install npm -g
Understanding this example

This application uses computer vision and augmented reality techniques to detect a chroma in a WebRTC stream based on color tracking.

The interface of the application (an HTML web page) is composed by two HTML5 video tags: one for the video camera stream (the local client-side stream) and other for the mirror (the remote stream). The video camera stream is sent to Kurento Media Server, which processes and sends it back to the client as a remote stream. To implement this, we need to create a Media Pipeline composed by the following Media Element s:

WebRTC with Chroma filter Media Pipeline

WebRTC with Chroma filter Media Pipeline

The complete source code of this demo can be found in GitHub.

This example is a modified version of the Magic Mirror tutorial. In this case, this demo uses a Chroma instead of FaceOverlay filter.

In order to perform chroma detection, there must be a color calibration stage. To accomplish this step, at the beginning of the demo, a little square appears in upper left of the video, as follows:

Chroma calibration stage

Chroma calibration stage

In the first second of the demo, a calibration process is done, by detecting the color inside that square. When the calibration is finished, the square disappears and the chroma is substituted with the configured image. Take into account that this process requires lighting condition. Otherwise the chroma substitution will not be perfect. This behavior can be seen in the upper right corner of the following screenshot:

Chroma filter in action

Chroma filter in action

注解

Modules can have options. For configuring these options, you’ll need to get the constructor for them. In Javascript and Node, you have to use kurentoClient.getComplexType(‘qualifiedName’) . There is an example in the code.

The media pipeline of this demo is is implemented in the JavaScript logic as follows:

...
kurento.register('kurento-module-chroma');
...

function start(sessionId, ws, sdpOffer, callback) {
    if (!sessionId) {
        return callback('Cannot use undefined sessionId');
    }

    getKurentoClient(function(error, kurentoClient) {
        if (error) {
            return callback(error);
        }

        kurentoClient.create('MediaPipeline', function(error, pipeline) {
            if (error) {
                return callback(error);
            }

            createMediaElements(pipeline, ws, function(error, webRtcEndpoint, filter) {
                if (error) {
                    pipeline.release();
                    return callback(error);
                }

                if (candidatesQueue[sessionId]) {
                    while(candidatesQueue[sessionId].length) {
                        var candidate = candidatesQueue[sessionId].shift();
                        webRtcEndpoint.addIceCandidate(candidate);
                    }
                }

                connectMediaElements(webRtcEndpoint, filter, function(error) {
                    if (error) {
                        pipeline.release();
                        return callback(error);
                    }

                    webRtcEndpoint.on('OnIceCandidate', function(event) {
                        var candidate = kurento.getComplexType('IceCandidate')(event.candidate);
                        ws.send(JSON.stringify({
                            id : 'iceCandidate',
                            candidate : candidate
                        }));
                    });

                    webRtcEndpoint.processOffer(sdpOffer, function(error, sdpAnswer) {
                        if (error) {
                            pipeline.release();
                            return callback(error);
                        }

                        sessions[sessionId] = {
                            'pipeline' : pipeline,
                            'webRtcEndpoint' : webRtcEndpoint
                        }
                        return callback(null, sdpAnswer);
                    });

                    webRtcEndpoint.gatherCandidates(function(error) {
                        if (error) {
                            return callback(error);
                        }
                    });
                });
            });
        });
    });
}

function createMediaElements(pipeline, ws, callback) {
    pipeline.create('WebRtcEndpoint', function(error, webRtcEndpoint) {
        if (error) {
            return callback(error);
        }

        var options = {
            window: kurento.getComplexType('chroma.WindowParam')({
                topRightCornerX: 5,
                topRightCornerY: 5,
                width: 30,
                height: 30
            })
        }
        pipeline.create('chroma.ChromaFilter', options, function(error, filter) {
            if (error) {
                return callback(error);
            }

            return callback(null, webRtcEndpoint, filter);
        });
    });
}

function connectMediaElements(webRtcEndpoint, filter, callback) {
    webRtcEndpoint.connect(filter, function(error) {
        if (error) {
            return callback(error);
        }

        filter.setBackground(url.format(asUrl) + 'img/mario.jpg', function(error) {
            if (error) {
                return callback(error);
            }

            filter.connect(webRtcEndpoint, function(error) {
                if (error) {
                    return callback(error);
                }

                return callback(null);
            });
        });
    });
}
Dependencies

Dependencies of this demo are managed using NPM. Our main dependency is the Kurento Client JavaScript (kurento-client). The relevant part of the package.json file for managing this dependency is:

"dependencies": {
   "kurento-client" : "6.6.0"
}

At the client side, dependencies are managed using Bower. Take a look to the bower.json file and pay attention to the following section:

"dependencies": {
   "kurento-utils" : "6.6.2",
   "kurento-module-pointerdetector": "6.6.0"
}

注解

We are in active development. You can find the latest versions at npm and Bower.

Module Tutorial - Crowd Detector Filter

This web application consists on a WebRTC video communication in mirror (loopback) with a crowd detector filter. This filter detects people agglomeration in video streams.

Java Module - Crowd Detector Filter

This web application consists on a WebRTC video communication in mirror (loopback) with a crowd detector filter. This filter detects clusters of people in video streams.

注解

This tutorial has been configured to use https. Follow the instructions to secure your application.

For the impatient: running this example

First of all, you should install Kurento Media Server to run this demo. Please visit the installation guide for further information. In addition, the built-in module kms-crowddetector-6.0 should be also installed:

sudo apt-get install kms-crowddetector-6.0

To launch the application, you need to clone the GitHub project where this demo is hosted, and then run the main class:

git clone https://github.com/Kurento/kurento-tutorial-java.git
cd kurento-tutorial-java/kurento-crowddetector
git checkout 6.6.2
mvn compile exec:java

The web application starts on port 8443 in the localhost by default. Therefore, open the URL https://localhost:8443/ in a WebRTC compliant browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the flag kms.url to the JVM executing the demo. As we’ll be using maven, you should execute the following command

mvn compile exec:java -Dkms.url=ws://kms_host:kms_port/kurento
Understanding this example

This application uses computer vision and augmented reality techniques to detect a crowd in a WebRTC stream.

The interface of the application (an HTML web page) is composed by two HTML5 video tags: one for the video camera stream (the local client-side stream) and other for the mirror (the remote stream). The video camera stream is sent to Kurento Media Server, which processes and sends it back to the client as a remote stream. To implement this, we need to create a Media Pipeline composed by the following Media Element s:

WebRTC with crowdDetector filter Media Pipeline

WebRTC with crowdDetector filter Media Pipeline

The complete source code of this demo can be found in GitHub.

This example is a modified version of the Magic Mirror tutorial. In this case, this demo uses a CrowdDetector instead of FaceOverlay filter.

To setup a CrowdDetectorFilter, first we need to define one or more regions of interest (ROIs). A ROI determines the zone within the video stream, which are going to be monitored and analised by the filter. To define a ROI, we need to configure at least three points. These points are defined in relative terms (0 to 1) to the video width and height.

CrowdDetectorFilter performs two actions in the defined ROIs. On one hand, the detected crowds are colored over the stream. On the other hand, different events are raised to the client.

To understand crowd coloring, we can take a look to an screenshot of a running example of CrowdDetectorFilter. In the picture below, we can see that there are two ROIs (bounded with white lines in the video). On these ROIs, we can see two different colors over the original video stream: red zones are drawn over detected static crowds (or moving slowly). Blue zones are drawn over the detected crowds moving fast.

Crowd detection sample

Crowd detection sample

Regarding crowd events, there are three types of events, namely:

  • CrowdDetectorFluidityEvent. Event raised when a certain level of fluidity is detected in a ROI. Fluidity can be seen as the level of general movement in a crowd.
  • CrowdDetectorOccupancyEvent. Event raised when a level of occupancy is detected in a ROI. Occupancy can be seen as the level of agglomeration in stream.
  • CrowdDetectorDirectionEvent. Event raised when a movement direction is detected in a ROI by a crowd.

Both fluidity as occupancy are quantified in a relative metric from 0 to 100%. Then, both attributes are qualified into three categories: i) Minimum (min); ii) Medium (med); iii) Maximum (max).

Regarding direction, it is quantified as an angle (0-360º), where 0 is the direction from the central point of the video to the top (i.e., north), 90 correspond to the direction to the right (east), 180 is the south, and finally 270 is the west.

With all these concepts, now we can check out the Java server-side code of this demo. As depicted in the snippet below, we create a ROI by adding RelativePoint instances to a list. Each ROI is then stored into a list of RegionOfInterest instances.

Then, each ROI should be configured. To do that, we have the following methods:

  • setFluidityLevelMin: Fluidity level (0-100%) for the category minimum.
  • setFluidityLevelMed: Fluidity level (0-100%) for the category medium.
  • setFluidityLevelMax: Fluidity level (0-100%) for the category maximum.
  • setFluidityNumFramesToEvent: Number of consecutive frames detecting a fluidity level to rise a event.
  • setOccupancyLevelMin: Occupancy level (0-100%) for the category minimum.
  • setOccupancyLevelMed: Occupancy level (0-100%) for the category medium.
  • setOccupancyLevelMax: Occupancy level (0-100%) for the category maximum.
  • setOccupancyNumFramesToEvent: Number of consecutive frames detecting a occupancy level to rise a event.
  • setSendOpticalFlowEvent: Boolean value that indicates whether or not directions events are going to be tracked by the filter. Be careful with this feature, since it is very demanding in terms of resource usage (CPU, memory) in the media server. Set to true this parameter only when you are going to need directions events in your client-side.
  • setOpticalFlowNumFramesToEvent: Number of consecutive frames detecting a direction level to rise a event.
  • setOpticalFlowNumFramesToReset: Number of consecutive frames detecting a occupancy level in which the counter is reset.
  • setOpticalFlowAngleOffset: Counterclockwise offset of the angle. This parameters is useful to move the default axis for directions (0º=north, 90º=east, 180º=south, 270º=west).

All in all, the media pipeline of this demo is implemented as follows:

// Media Logic (Media Pipeline and Elements)
MediaPipeline pipeline = kurento.createMediaPipeline();
pipelines.put(session.getId(), pipeline);

WebRtcEndpoint webRtcEndpoint = new WebRtcEndpoint.Builder(pipeline)
      .build();
webRtcEndpoint
   .addIceCandidateFoundListener(new EventListener<IceCandidateFoundEvent>() {
      @Override
      public void onEvent(IceCandidateFoundEvent event) {
      JsonObject response = new JsonObject();
      response.addProperty("id", "iceCandidate");
      response.add("candidate",
         JsonUtils.toJsonObject(event.getCandidate()));
      try {
         synchronized (session) {
         session.sendMessage(new TextMessage(response
            .toString()));
         }
      } catch (IOException e) {
         log.debug(e.getMessage());
      }
      }
   });

List<RegionOfInterest> rois = new ArrayList<>();
List<RelativePoint> points = new ArrayList<RelativePoint>();

points.add(new RelativePoint(0, 0));
points.add(new RelativePoint(0.5F, 0));
points.add(new RelativePoint(0.5F, 0.5F));
points.add(new RelativePoint(0, 0.5F));

RegionOfInterestConfig config = new RegionOfInterestConfig();

config.setFluidityLevelMin(10);
config.setFluidityLevelMed(35);
config.setFluidityLevelMax(65);
config.setFluidityNumFramesToEvent(5);
config.setOccupancyLevelMin(10);
config.setOccupancyLevelMed(35);
config.setOccupancyLevelMax(65);
config.setOccupancyNumFramesToEvent(5);
config.setSendOpticalFlowEvent(false);
config.setOpticalFlowNumFramesToEvent(3);
config.setOpticalFlowNumFramesToReset(3);
config.setOpticalFlowAngleOffset(0);

rois.add(new RegionOfInterest(points, config, "roi0"));

CrowdDetectorFilter crowdDetectorFilter = new CrowdDetectorFilter.Builder(
      pipeline, rois).build();

webRtcEndpoint.connect(crowdDetectorFilter);
crowdDetectorFilter.connect(webRtcEndpoint);

// addEventListener to crowddetector
crowdDetectorFilter.addCrowdDetectorDirectionListener(
   new EventListener<CrowdDetectorDirectionEvent>() {
   @Override
   public void onEvent(CrowdDetectorDirectionEvent event) {
      JsonObject response = new JsonObject();
      response.addProperty("id", "directionEvent");
      response.addProperty("roiId", event.getRoiID());
      response.addProperty("angle",
      event.getDirectionAngle());
      try {
         session.sendMessage(new TextMessage(response
         .toString()));
      } catch (Throwable t) {
         sendError(session, t.getMessage());
      }
   }
      });

crowdDetectorFilter.addCrowdDetectorFluidityListener(
   new EventListener<CrowdDetectorFluidityEvent>() {
   @Override
   public void onEvent(CrowdDetectorFluidityEvent event) {
      JsonObject response = new JsonObject();
      response.addProperty("id", "fluidityEvent");
      response.addProperty("roiId", event.getRoiID());
      response.addProperty("level",
      event.getFluidityLevel());
      response.addProperty("percentage",
      event.getFluidityPercentage());
      try {
         session.sendMessage(new TextMessage(response
         .toString()));
      } catch (Throwable t) {
         sendError(session, t.getMessage());
      }
   }
      });

crowdDetectorFilter.addCrowdDetectorOccupancyListener(
   new EventListener<CrowdDetectorOccupancyEvent>() {
   @Override
   public void onEvent(CrowdDetectorOccupancyEvent event) {
      JsonObject response = new JsonObject();
      response.addProperty("id", "occupancyEvent");
      response.addProperty("roiId", event.getRoiID());
      response.addProperty("level",
      event.getOccupancyLevel());
      response.addProperty("percentage",
      event.getOccupancyPercentage());
      try {
         session.sendMessage(new TextMessage(response
         .toString()));
      } catch (Throwable t) {
         sendError(session, t.getMessage());
      }
   }
      });

// SDP negotiation (offer and answer)
String sdpOffer = jsonMessage.get("sdpOffer").getAsString();
String sdpAnswer = webRtcEndpoint.processOffer(sdpOffer);

// Sending response back to client
JsonObject response = new JsonObject();
response.addProperty("id", "startResponse");
response.addProperty("sdpAnswer", sdpAnswer);
session.sendMessage(new TextMessage(response.toString()));

webRtcEndpoint.gatherCandidates();
Dependencies

This Java Spring application is implemented using Maven. The relevant part of the pom.xml is where Kurento dependencies are declared. As the following snippet shows, we need two dependencies: the Kurento Client Java dependency (kurento-client) and the JavaScript Kurento utility library (kurento-utils) for the client-side. Other client libraries are managed with webjars:

<dependencies>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-client</artifactId>
   </dependency>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-utils-js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars</groupId>
      <artifactId>webjars-locator</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>bootstrap</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>demo-console</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>adapter.js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>jquery</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>ekko-lightbox</artifactId>
   </dependency>
</dependencies>

注解

We are in active development. You can find the latest version of Kurento Java Client at Maven Central.

Kurento Java Client has a minimum requirement of Java 7. Hence, you need to include the following properties in your pom:

<maven.compiler.target>1.7</maven.compiler.target>
<maven.compiler.source>1.7</maven.compiler.source>
JavaScript Module - Crowd Detector Filter

This web application consists on a WebRTC video communication in mirror (loopback) with a crowd detector filter. This filter detects people agglomeration in video streams.

注解

This tutorial has been configurated for using https. Follow these instructions for securing your application.

For the impatient: running this example

First of all, you should install Kurento Media Server to run this demo. Please visit the installation guide for further information. In addition, the built-in module kms-crowddetector-6.0 should be also installed:

sudo apt-get install kms-crowddetector-6.0

Be sure to have installed Node.js and Bower in your system. In an Ubuntu machine, you can install both as follows:

curl -sL https://deb.nodesource.com/setup_4.x | sudo bash -
sudo apt-get install -y nodejs
sudo npm install -g bower

Due to Same-origin policy, this demo has to be served by an HTTP server. A very simple way of doing this is by means of an HTTP Node.js server which can be installed using npm :

sudo npm install http-server -g

You also need the source code of this demo. You can clone it from GitHub. Then start the HTTP server:

git clone https://github.com/Kurento/kurento-tutorial-js.git
cd kurento-tutorial-js/kurento-crowddetector
git checkout 6.6.1
bower install
http-server -p 8443 -S -C keys/server.crt -K keys/server.key

Finally, access the application connecting to the URL https://localhost:8443/ through a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. Kurento Media Server must use WebSockets over SSL/TLS (WSS), so make sure you check this too. It is possible to locate the KMS in other machine simple adding the parameter ws_uri to the URL:

https://localhost:8443/index.html?ws_uri=wss://kms_host:kms_port/kurento

Notice that the Kurento Media Server must connected using a Secure WebSocket (i.e., the KMS URI starts with wss://). For this reason, the support for secure WebSocket must be enabled in the Kurento Media Server you are using to run this tutorial. For further information about securing applications, please visit the following page.

Understanding this example

This application uses computer vision and augmented reality techniques to detect a crowd in a WebRTC stream.

The interface of the application (an HTML web page) is composed by two HTML5 video tags: one for the video camera stream (the local client-side stream) and other for the mirror (the remote stream). The video camera stream is sent to Kurento Media Server, which processes and sends it back to the client as a remote stream. To implement this, we need to create a Media Pipeline composed by the following Media Element s:

WebRTC with crowdDetector filter Media Pipeline

WebRTC with crowdDetector filter Media Pipeline

The complete source code of this demo can be found in GitHub.

This example is a modified version of the Magic Mirror tutorial. In this case, this demo uses a CrowdDetector instead of FaceOverlay filter.

To setup a CrowdDetectorFilter, first we need to define one or more region of interests (ROIs). A ROI delimits the zone within the video stream in which crowd are going to be tracked. To define a ROI, we need to configure at least three points. These points are defined in relative terms (0 to 1) to the video width and height.

CrowdDetectorFilter performs two actions in the defined ROIs. On the one hand, the detected crowd are colored over the stream. On the other hand, different events are raised to the client.

To understand crowd coloring, we can take a look to an screenshot of a running example of CrowdDetectorFilter. In the picture below, we can see that there are two ROIs (bounded with white lines in the video). On these ROIs, we can see two different colors over the original video stream: red zones are drawn over detected static crowds (or moving slowly). Blue zones are drawn over the detected crowds moving fast.

Crowd detection sample

Crowd detection sample

Regarding crowd events, there are three types of events, namely:

  • CrowdDetectorFluidityEvent. Event raised when a certain level of fluidity is detected in a ROI. Fluidity can be seen as the level of general movement in a crowd.
  • CrowdDetectorOccupancyEvent. Event raised when a level of occupancy is detected in a ROI. Occupancy can be seen as the level of agglomeration in stream.
  • CrowdDetectorDirectionEvent. Event raised when a movement direction is detected in a ROI by a crowd.

Both fluidity as occupancy are quantified in a relative metric from 0 to 100%. Then, both attributes are qualified into three categories: i) Minimum (min); ii) Medium (med); iii) Maximum (max).

Regarding direction, it is quantified as an angle (0-360º), where 0 is the direction from the central point of the video to the top (i.e., north), 90 correspond to the direction to the right (east), 180 is the south, and finally 270 is the west.

With all these concepts, now we can check out the Java server-side code of this demo. As depicted in the snippet below, we create a ROI by adding RelativePoint instances to a list. Each ROI is then stored into a list of RegionOfInterest instances.

Then, each ROI should be configured. To do that, we have the following methods:

  • fluidityLevelMin: Fluidity level (0-100%) for the category minimum.
  • fluidityLevelMed: Fluidity level (0-100%) for the category medium.
  • fluidityLevelMax: Fluidity level (0-100%) for the category maximum.
  • fluidityNumFramesToEvent: Number of consecutive frames detecting a fluidity level to rise a event.
  • occupancyLevelMin: Occupancy level (0-100%) for the category minimum.
  • occupancyLevelMed: Occupancy level (0-100%) for the category medium.
  • occupancyLevelMax: Occupancy level (0-100%) for the category maximum.
  • occupancyNumFramesToEvent: Number of consecutive frames detecting a occupancy level to rise a event.
  • sendOpticalFlowEvent: Boolean value that indicates whether or not directions events are going to be tracked by the filter. Be careful with this feature, since it is very demanding in terms of resource usage (CPU, memory) in the media server. Set to true this parameter only when you are going to need directions events in your client-side.
  • opticalFlowNumFramesToEvent: Number of consecutive frames detecting a direction level to rise a event.
  • opticalFlowNumFramesToReset: Number of consecutive frames detecting a occupancy level in which the counter is reset.
  • opticalFlowAngleOffset: Counterclockwise offset of the angle. This parameters is useful to move the default axis for directions (0º=north, 90º=east, 180º=south, 270º=west).

注解

Modules can have options. For configuring these options, you’ll need to get the constructor for them. In Javascript and Node, you have to use kurentoClient.getComplexType(‘qualifiedName’) . There is an example in the code.

All in all, the media pipeline of this demo is is implemented as follows:

...
kurentoClient.register('kurento-module-crowddetector')
const RegionOfInterest       = kurentoClient.getComplexType('crowddetector.RegionOfInterest')
const RegionOfInterestConfig = kurentoClient.getComplexType('crowddetector.RegionOfInterestConfig')
const RelativePoint          = kurentoClient.getComplexType('crowddetector.RelativePoint')
...

kurentoClient(args.ws_uri, function(error, client) {
  if (error) return onError(error);

  client.create('MediaPipeline', function(error, p) {
    if (error) return onError(error);

    pipeline = p;

    console.log("Got MediaPipeline");

    pipeline.create('WebRtcEndpoint', function(error, webRtc) {
      if (error) return onError(error);

      console.log("Got WebRtcEndpoint");

      setIceCandidateCallbacks(webRtcPeer, webRtc, onError)

      webRtc.processOffer(sdpOffer, function(error, sdpAnswer) {
        if (error) return onError(error);

        console.log("SDP answer obtained. Processing ...");

        webRtc.gatherCandidates(onError);

        webRtcPeer.processAnswer(sdpAnswer);
      });

      var options =
      {
        rois:
        [
          RegionOfInterest({
            id: 'roi1',
            points:
            [
              RelativePoint({x: 0,   y: 0}),
              RelativePoint({x: 0.5, y: 0}),
              RelativePoint({x: 0.5, y: 0.5}),
              RelativePoint({x: 0,   y: 0.5})
            ],
            regionOfInterestConfig: RegionOfInterestConfig({
              occupancyLevelMin: 10,
              occupancyLevelMed: 35,
              occupancyLevelMax: 65,
              occupancyNumFramesToEvent: 5,
              fluidityLevelMin: 10,
              fluidityLevelMed: 35,
              fluidityLevelMax: 65,
              fluidityNumFramesToEvent: 5,
              sendOpticalFlowEvent: false,
              opticalFlowNumFramesToEvent: 3,
              opticalFlowNumFramesToReset: 3,
              opticalFlowAngleOffset: 0
            })
          })
        ]
      }

      pipeline.create('crowddetector.CrowdDetectorFilter', options, function(error, filter)
      {
        if (error) return onError(error);

        console.log("Connecting...");

        filter.on('CrowdDetectorDirection', function (data){
          console.log("Direction event received in roi " + data.roiID +
             " with direction " + data.directionAngle);
        });

        filter.on('CrowdDetectorFluidity', function (data){
          console.log("Fluidity event received in roi " + data.roiID +
           ". Fluidity level " + data.fluidityPercentage +
           " and fluidity percentage " + data.fluidityLevel);
        });

        filter.on('CrowdDetectorOccupancy', function (data){
          console.log("Occupancy event received in roi " + data.roiID +
           ". Occupancy level " + data.occupancyPercentage +
           " and occupancy percentage " + data.occupancyLevel);
        });

        client.connect(webRtc, filter, webRtc, function(error){
          if (error) return onError(error);

          console.log("WebRtcEndpoint --> Filter --> WebRtcEndpoint");
        });
      });
    });
  });
});

注解

The TURN and STUN servers to be used can be configured simple adding the parameter ice_servers to the application URL, as follows:

https://localhost:8443/index.html?ice_servers=[{"urls":"stun:stun1.example.net"},{"urls":"stun:stun2.example.net"}]
https://localhost:8443/index.html?ice_servers=[{"urls":"turn:turn.example.org","username":"user","credential":"myPassword"}]
Dependencies

The dependencies of this demo has to be obtained using Bower. The definition of these dependencies are defined in the bower.json file, as follows:

"dependencies": {
   "kurento-client": "6.6.0",
   "kurento-utils": "6.6.2"
   "kurento-module-pointerdetector": "6.6.0"
}

To get these dependencies, just run the following shell command:

bower install

注解

We are in active development. You can find the latest versions at Bower.

Node.js Module - Crowd Detector Filter

This web application consists on a WebRTC video communication in mirror (loopback) with a crowd detector filter. This filter detects people agglomeration in video streams.

注解

This tutorial has been configurated for using https. Follow these instructions for securing your application.

For the impatient: running this example

First of all, you should install Kurento Media Server to run this demo. Please visit the installation guide for further information. In addition, the built-in module kms-crowddetector-6.0 should be also installed:

sudo apt-get install kms-crowddetector-6.0

Be sure to have installed Node.js and Bower in your system. In an Ubuntu machine, you can install both as follows:

curl -sL https://deb.nodesource.com/setup_4.x | sudo bash -
sudo apt-get install -y nodejs
sudo npm install -g bower

To launch the application, you need to clone the GitHub project where this demo is hosted, install it and run it:

git clone https://github.com/Kurento/kurento-tutorial-node.git
cd kurento-tutorial-node/kurento-crowddetector
git checkout 6.6.1
npm install

If you have problems installing any of the dependencies, please remove them and clean the npm cache, and try to install them again:

rm -r node_modules
npm cache clean

Finally, access the application connecting to the URL https://localhost:8443/ through a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the argument ws_uri to the npm execution command, as follows:

npm start -- --ws_uri=ws://kms_host:kms_port/kurento

In this case you need to use npm version 2. To update it you can use this command:

sudo npm install npm -g
Understanding this example

This application uses computer vision and augmented reality techniques to detect a crowd in a WebRTC stream.

The interface of the application (an HTML web page) is composed by two HTML5 video tags: one for the video camera stream (the local client-side stream) and other for the mirror (the remote stream). The video camera stream is sent to Kurento Media Server, which processes and sends it back to the client as a remote stream. To implement this, we need to create a Media Pipeline composed by the following Media Element s:

WebRTC with crowdDetector filter Media Pipeline

WebRTC with crowdDetector filter Media Pipeline

The complete source code of this demo can be found in GitHub.

This example is a modified version of the Magic Mirror tutorial. In this case, this demo uses a CrowdDetector instead of FaceOverlay filter.

To setup a CrowdDetectorFilter, first we need to define one or more region of interests (ROIs). A ROI delimits the zone within the video stream in which crowd are going to be tracked. To define a ROI, we need to configure at least three points. These points are defined in relative terms (0 to 1) to the video width and height.

CrowdDetectorFilter performs two actions in the defined ROIs. On the one hand, the detected crowd are colored over the stream. On the other hand, different events are raised to the client.

To understand crowd coloring, we can take a look to an screenshot of a running example of CrowdDetectorFilter. In the picture below, we can see that there are two ROIs (bounded with white lines in the video). On these ROIs, we can see two different colors over the original video stream: red zones are drawn over detected static crowds (or moving slowly). Blue zones are drawn over the detected crowds moving fast.

Crowd detection sample

Crowd detection sample

Regarding crowd events, there are three types of events, namely:

  • CrowdDetectorFluidityEvent. Event raised when a certain level of fluidity is detected in a ROI. Fluidity can be seen as the level of general movement in a crowd.
  • CrowdDetectorOccupancyEvent. Event raised when a level of occupancy is detected in a ROI. Occupancy can be seen as the level of agglomeration in stream.
  • CrowdDetectorDirectionEvent. Event raised when a movement direction is detected in a ROI by a crowd.

Both fluidity as occupancy are quantified in a relative metric from 0 to 100%. Then, both attributes are qualified into three categories: i) Minimum (min); ii) Medium (med); iii) Maximum (max).

Regarding direction, it is quantified as an angle (0-360º), where 0 is the direction from the central point of the video to the top (i.e., north), 90 correspond to the direction to the right (east), 180 is the south, and finally 270 is the west.

With all these concepts, now we can check out the Java server-side code of this demo. As depicted in the snippet below, we create a ROI by adding RelativePoint instances to a list. Each ROI is then stored into a list of RegionOfInterest instances.

Then, each ROI should be configured. To do that, we have the following methods:

  • fluidityLevelMin: Fluidity level (0-100%) for the category minimum.
  • fluidityLevelMed: Fluidity level (0-100%) for the category medium.
  • fluidityLevelMax: Fluidity level (0-100%) for the category maximum.
  • fluidityNumFramesToEvent: Number of consecutive frames detecting a fluidity level to rise a event.
  • occupancyLevelMin: Occupancy level (0-100%) for the category minimum.
  • occupancyLevelMed: Occupancy level (0-100%) for the category medium.
  • occupancyLevelMax: Occupancy level (0-100%) for the category maximum.
  • occupancyNumFramesToEvent: Number of consecutive frames detecting a occupancy level to rise a event.
  • sendOpticalFlowEvent: Boolean value that indicates whether or not directions events are going to be tracked by the filter. Be careful with this feature, since it is very demanding in terms of resource usage (CPU, memory) in the media server. Set to true this parameter only when you are going to need directions events in your client-side.
  • opticalFlowNumFramesToEvent: Number of consecutive frames detecting a direction level to rise a event.
  • opticalFlowNumFramesToReset: Number of consecutive frames detecting a occupancy level in which the counter is reset.
  • opticalFlowAngleOffset: Counterclockwise offset of the angle. This parameters is useful to move the default axis for directions (0º=north, 90º=east, 180º=south, 270º=west).

注解

Modules can have options. For configuring these options, you’ll need to get the constructor for them. In Javascript and Node, you have to use kurentoClient.getComplexType(‘qualifiedName’) . There is an example in the code.

All in all, the media pipeline of this demo is is implemented as follows:

...
kurento.register('kurento-module-crowddetector');
const RegionOfInterest       = kurento.getComplexType('crowddetector.RegionOfInterest');
const RegionOfInterestConfig = kurento.getComplexType('crowddetector.RegionOfInterestConfig');
const RelativePoint          = kurento.getComplexType('crowddetector.RelativePoint');
...

function start(sessionId, ws, sdpOffer, callback) {
    if (!sessionId) {
        return callback('Cannot use undefined sessionId');
    }

    getKurentoClient(function(error, kurentoClient) {
        if (error) {
            return callback(error);
        }

        kurentoClient.create('MediaPipeline', function(error, pipeline) {
            if (error) {
                return callback(error);
            }

            createMediaElements(pipeline, ws, function(error, webRtcEndpoint, filter) {
                if (error) {
                    pipeline.release();
                    return callback(error);
                }

                if (candidatesQueue[sessionId]) {
                    while(candidatesQueue[sessionId].length) {
                        var candidate = candidatesQueue[sessionId].shift();
                        webRtcEndpoint.addIceCandidate(candidate);
                    }
                }

                connectMediaElements(webRtcEndpoint, filter, function(error) {
                    if (error) {
                        pipeline.release();
                        return callback(error);
                    }

                    filter.on('CrowdDetectorDirection', function (_data){
                        return callback(null, 'crowdDetectorDirection', _data);
                    });

                    filter.on('CrowdDetectorFluidity', function (_data){
                        return callback(null, 'crowdDetectorFluidity', _data);
                    });

                    filter.on('CrowdDetectorOccupancy', function (_data){
                        return callback(null, 'crowdDetectorOccupancy', _data);
                    });

                    webRtcEndpoint.on('OnIceCandidate', function(event) {
                        var candidate = kurento.getComplexType('IceCandidate')(event.candidate);
                        ws.send(JSON.stringify({
                            id : 'iceCandidate',
                            candidate : candidate
                        }));
                    });

                    webRtcEndpoint.processOffer(sdpOffer, function(error, sdpAnswer) {
                        if (error) {
                            pipeline.release();
                            return callback(error);
                        }

                        sessions[sessionId] = {
                            'pipeline' : pipeline,
                            'webRtcEndpoint' : webRtcEndpoint
                        }
                        return callback(null, 'sdpAnswer', sdpAnswer);
                    });

                    webRtcEndpoint.gatherCandidates(function(error) {
                        if (error) {
                            return callback(error);
                        }
                    });
                });
            });
        });
    });
}

function createMediaElements(pipeline, ws, callback) {
    pipeline.create('WebRtcEndpoint', function(error, webRtcEndpoint) {
        if (error) {
            return callback(error);
        }

        var options = {
          rois: [
            RegionOfInterest({
              id: 'roi1',
              points: [
                RelativePoint({x: 0  , y: 0  }),
                RelativePoint({x: 0.5, y: 0  }),
                RelativePoint({x: 0.5, y: 0.5}),
                RelativePoint({x: 0  , y: 0.5})
              ],
              regionOfInterestConfig: RegionOfInterestConfig({
                occupancyLevelMin: 10,
                occupancyLevelMed: 35,
                occupancyLevelMax: 65,
                occupancyNumFramesToEvent: 5,
                fluidityLevelMin: 10,
                fluidityLevelMed: 35,
                fluidityLevelMax: 65,
                fluidityNumFramesToEvent: 5,
                sendOpticalFlowEvent: false,
                opticalFlowNumFramesToEvent: 3,
                opticalFlowNumFramesToReset: 3,
                opticalFlowAngleOffset: 0
              })
            })
          ]
        }
        pipeline.create('crowddetector.CrowdDetectorFilter', options, function(error, filter) {
            if (error) {
                return callback(error);
            }

            return callback(null, webRtcEndpoint, filter);
        });
    });
}
Dependencies

Dependencies of this demo are managed using NPM. Our main dependency is the Kurento Client JavaScript (kurento-client). The relevant part of the package.json file for managing this dependency is:

"dependencies": {
   "kurento-client" : "6.6.0"
}

At the client side, dependencies are managed using Bower. Take a look to the bower.json file and pay attention to the following section:

"dependencies": {
   "kurento-utils" : "6.6.2",
   "kurento-module-pointerdetector": "6.6.0"
}

注解

We are in active development. You can find the latest versions at npm and Bower.

Module Tutorial - Plate Detector Filter

This web application consists on a WebRTC video communication in mirror (loopback) with a plate detector filter element.

Java Module - Plate Detector Filter

This web application consists on a WebRTC video communication in mirror (loopback) with a plate detector filter element.

注解

This tutorial has been configured to use https. Follow the instructions to secure your application.

For the impatient: running this example

First of all, you should install Kurento Media Server to run this demo. Please visit the installation guide for further information. In addition, the built-in module kms-platedetector-6.0 should be also installed:

sudo apt-get install kms-platedetector-6.0

警告

Plate detector module is a prototype and its results is not always accurate. Consider this if you are planning to use this module in a production environment.

To launch the application, you need to clone the GitHub project where this demo is hosted, and then run the main class:

git clone https://github.com/Kurento/kurento-tutorial-java.git
cd kurento-tutorial-java/kurento-platedetector
git checkout 6.6.2
mvn compile exec:java

The web application starts on port 8443 in the localhost by default. Therefore, open the URL https://localhost:8443/ in a WebRTC compliant browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the flag kms.url to the JVM executing the demo. As we’ll be using maven, you should execute the following command

mvn compile exec:java -Dkms.url=ws://kms_host:kms_port/kurento
Understanding this example

This application uses computer vision and augmented reality techniques to detect a plate in a WebRTC stream on optical character recognition (OCR).

The interface of the application (an HTML web page) is composed by two HTML5 video tags: one for the video camera stream (the local client-side stream) and other for the mirror (the remote stream). The video camera stream is sent to Kurento Media Server, which processes and sends it back to the client as a remote stream. To implement this, we need to create a Media Pipeline composed by the following Media Element s:

WebRTC with plateDetector filter Media Pipeline

WebRTC with plateDetector filter Media Pipeline

The complete source code of this demo can be found in GitHub.

This example is a modified version of the Magic Mirror tutorial. In this case, this demo uses a PlateDetector instead of FaceOverlay filter. A screenshot of the running example is shown in the following picture:

Plate detector demo in action

Plate detector demo in action

The following snippet shows how the media pipeline is implemented in the Java server-side code of the demo. An important issue in this code is that a listener is added to the PlateDetectorFilter object (addPlateDetectedListener). This way, each time a plate is detected in the stream, a message is sent to the client side. As shown in the screenshot below, this event is printed in the console of the GUI.

private void start(final WebSocketSession session, JsonObject jsonMessage) {
   try {
      // Media Logic (Media Pipeline and Elements)
      UserSession user = new UserSession();
      MediaPipeline pipeline = kurento.createMediaPipeline();
      user.setMediaPipeline(pipeline);
      WebRtcEndpoint webRtcEndpoint = new WebRtcEndpoint.Builder(pipeline)
            .build();
      user.setWebRtcEndpoint(webRtcEndpoint);
      users.put(session.getId(), user);

      webRtcEndpoint
            .addIceCandidateFoundListener(new EventListener<IceCandidateFoundEvent>() {

               @Override
               public void onEvent(IceCandidateFoundEvent event) {
                  JsonObject response = new JsonObject();
                  response.addProperty("id", "iceCandidate");
                  response.add("candidate", JsonUtils
                        .toJsonObject(event.getCandidate()));
                  try {
                     synchronized (session) {
                        session.sendMessage(new TextMessage(
                              response.toString()));
                     }
                  } catch (IOException e) {
                     log.debug(e.getMessage());
                  }
               }
            });

      PlateDetectorFilter plateDetectorFilter = new PlateDetectorFilter.Builder(
            pipeline).build();

      webRtcEndpoint.connect(plateDetectorFilter);
      plateDetectorFilter.connect(webRtcEndpoint);

      plateDetectorFilter
            .addPlateDetectedListener(new EventListener<PlateDetectedEvent>() {
               @Override
               public void onEvent(PlateDetectedEvent event) {
                  JsonObject response = new JsonObject();
                  response.addProperty("id", "plateDetected");
                  response.addProperty("plate", event.getPlate());
                  try {
                     session.sendMessage(new TextMessage(response
                           .toString()));
                  } catch (Throwable t) {
                     sendError(session, t.getMessage());
                  }
               }
            });

      // SDP negotiation (offer and answer)
      String sdpOffer = jsonMessage.get("sdpOffer").getAsString();
      String sdpAnswer = webRtcEndpoint.processOffer(sdpOffer);

      // Sending response back to client
      JsonObject response = new JsonObject();
      response.addProperty("id", "startResponse");
      response.addProperty("sdpAnswer", sdpAnswer);

      synchronized (session) {
         session.sendMessage(new TextMessage(response.toString()));
      }
      webRtcEndpoint.gatherCandidates();
   } catch (Throwable t) {
      sendError(session, t.getMessage());
   }
}
Dependencies

This Java Spring application is implemented using Maven. The relevant part of the pom.xml is where Kurento dependencies are declared. As the following snippet shows, we need two dependencies: the Kurento Client Java dependency (kurento-client) and the JavaScript Kurento utility library (kurento-utils) for the client-side. Other client libraries are managed with webjars:

<dependencies>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-client</artifactId>
   </dependency>
   <dependency>
      <groupId>org.kurento</groupId>
      <artifactId>kurento-utils-js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars</groupId>
      <artifactId>webjars-locator</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>bootstrap</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>demo-console</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>adapter.js</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>jquery</artifactId>
   </dependency>
   <dependency>
      <groupId>org.webjars.bower</groupId>
      <artifactId>ekko-lightbox</artifactId>
   </dependency>
</dependencies>

注解

We are in active development. You can find the latest version of Kurento Java Client at Maven Central.

Kurento Java Client has a minimum requirement of Java 7. Hence, you need to include the following properties in your pom:

<maven.compiler.target>1.7</maven.compiler.target>
<maven.compiler.source>1.7</maven.compiler.source>
JavaScript Module - Plate Detector Filter

This web application consists on a WebRTC video communication in mirror (loopback) with a plate detector filter element.

注解

This tutorial has been configurated for using https. Follow these instructions for securing your application.

For the impatient: running this example

First of all, you should install Kurento Media Server to run this demo. Please visit the installation guide for further information. In addition, the built-in module kms-platedetector-6.0 should be also installed:

sudo apt-get install kms-platedetector-6.0

警告

Plate detector module is a prototype and its results is not always accurate. Consider this if you are planning to use this module in a production environment.

Be sure to have installed Node.js and Bower in your system. In an Ubuntu machine, you can install both as follows:

curl -sL https://deb.nodesource.com/setup_4.x | sudo bash -
sudo apt-get install -y nodejs
sudo npm install -g bower

Due to Same-origin policy, this demo has to be served by an HTTP server. A very simple way of doing this is by means of an HTTP Node.js server which can be installed using npm :

sudo npm install http-server -g

You also need the source code of this demo. You can clone it from GitHub. Then start the HTTP server:

git clone https://github.com/Kurento/kurento-tutorial-js.git
cd kurento-tutorial-js/kurento-platedetector
git checkout 6.6.1
bower install
http-server -p 8443 -S -C keys/server.crt -K keys/server.key

Finally, access the application connecting to the URL https://localhost:8443/ through a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. Kurento Media Server must use WebSockets over SSL/TLS (WSS), so make sure you check this too. It is possible to locate the KMS in other machine simple adding the parameter ws_uri to the URL:

https://localhost:8443/index.html?ws_uri=wss://kms_host:kms_port/kurento

Notice that the Kurento Media Server must connected using a Secure WebSocket (i.e., the KMS URI starts with wss://). For this reason, the support for secure WebSocket must be enabled in the Kurento Media Server you are using to run this tutorial. For further information about securing applications, please visit the following page.

Understanding this example

This application uses computer vision and augmented reality techniques to detect a plate in a WebRTC stream on optical character recognition (OCR).

The interface of the application (an HTML web page) is composed by two HTML5 video tags: one for the video camera stream (the local client-side stream) and other for the mirror (the remote stream). The video camera stream is sent to Kurento Media Server, which processes and sends it back to the client as a remote stream. To implement this, we need to create a Media Pipeline composed by the following Media Element s:

WebRTC with plateDetector filter Media Pipeline

WebRTC with plateDetector filter Media Pipeline

The complete source code of this demo can be found in GitHub.

This example is a modified version of the Magic Mirror tutorial. In this case, this demo uses a PlateDetector instead of FaceOverlay filter. An screenshot of the running example is shown in the following picture:

Plate detector demo in action

Plate detector demo in action

注解

Modules can have options. For configuring these options, you’ll need to get the constructor for them. In Javascript and Node, you have to use kurentoClient.getComplexType(‘qualifiedName’) . There is an example in the code.

The following snippet shows how the media pipeline is implemented in the Java server-side code of the demo. An important issue in this code is that a listener is added to the PlateDetectorFilter object (addPlateDetectedListener). This way, each time a plate is detected in the stream, a message is sent to the client side. As shown in the screenshot below, this event is printed in the console of the GUI.

...
kurentoClient.register('kurento-module-platedetector')
...

kurentoClient(args.ws_uri, function(error, client) {
  if (error) return onError(error);

  client.create('MediaPipeline', function(error, _pipeline) {
    if (error) return onError(error);

    pipeline = _pipeline;

    console.log("Got MediaPipeline");

    pipeline.create('WebRtcEndpoint', function(error, webRtc) {
      if (error) return onError(error);

      console.log("Got WebRtcEndpoint");

      setIceCandidateCallbacks(webRtcPeer, webRtc, onError)

      webRtc.processOffer(sdpOffer, function(error, sdpAnswer) {
        if (error) return onError(error);

        console.log("SDP answer obtained. Processing...");

        webRtc.gatherCandidates(onError);
        webRtcPeer.processAnswer(sdpAnswer);
      });

      pipeline.create('platedetector.PlateDetectorFilter', function(error, filter) {
        if (error) return onError(error);

        console.log("Got Filter");

        filter.on('PlateDetected', function (data){
          console.log("License plate detected " + data.plate);
        });

        client.connect(webRtc, filter, webRtc, function(error) {
          if (error) return onError(error);

          console.log("WebRtcEndpoint --> filter --> WebRtcEndpoint");
        });
      });
    });
  });
});

注解

The TURN and STUN servers to be used can be configured simple adding the parameter ice_servers to the application URL, as follows:

https://localhost:8443/index.html?ice_servers=[{"urls":"stun:stun1.example.net"},{"urls":"stun:stun2.example.net"}]
https://localhost:8443/index.html?ice_servers=[{"urls":"turn:turn.example.org","username":"user","credential":"myPassword"}]
Dependencies

The dependencies of this demo has to be obtained using Bower. The definition of these dependencies are defined in the bower.json file, as follows:

"dependencies": {
   "kurento-client": "6.6.0",
   "kurento-utils": "6.6.2"
   "kurento-module-pointerdetector": "6.6.0"
}

To get these dependencies, just run the following shell command:

bower install

注解

We are in active development. You can find the latest versions at Bower.

Node.js Module - Plate Detector Filter

This web application consists on a WebRTC video communication in mirror (loopback) with a plate detector filter element.

注解

This tutorial has been configurated for using https. Follow these instructions for securing your application.

For the impatient: running this example

First of all, you should install Kurento Media Server to run this demo. Please visit the installation guide for further information. In addition, the built-in module kms-platedetector-6.0 should be also installed:

sudo apt-get install kms-platedetector-6.0

警告

Plate detector module is a prototype and its results is not always accurate. Consider this if you are planning to use this module in a production environment.

Be sure to have installed Node.js and Bower in your system. In an Ubuntu machine, you can install both as follows:

curl -sL https://deb.nodesource.com/setup_4.x | sudo bash -
sudo apt-get install -y nodejs
sudo npm install -g bower

To launch the application, you need to clone the GitHub project where this demo is hosted, install it and run it:

git clone https://github.com/Kurento/kurento-tutorial-node.git
cd kurento-tutorial-node/kurento-platedetector
git checkout 6.6.1
npm install

If you have problems installing any of the dependencies, please remove them and clean the npm cache, and try to install them again:

rm -r node_modules
npm cache clean

Finally, access the application connecting to the URL https://localhost:8443/ through a WebRTC capable browser (Chrome, Firefox).

注解

These instructions work only if Kurento Media Server is up and running in the same machine as the tutorial. However, it is possible to connect to a remote KMS in other machine, simply adding the argument ws_uri to the npm execution command, as follows:

npm start -- --ws_uri=ws://kms_host:kms_port/kurento

In this case you need to use npm version 2. To update it you can use this command:

sudo npm install npm -g
Understanding this example

This application uses computer vision and augmented reality techniques to detect a plate in a WebRTC stream on optical character recognition (OCR).

The interface of the application (an HTML web page) is composed by two HTML5 video tags: one for the video camera stream (the local client-side stream) and other for the mirror (the remote stream). The video camera stream is sent to Kurento Media Server, which processes and sends it back to the client as a remote stream. To implement this, we need to create a Media Pipeline composed by the following Media Element s:

WebRTC with plateDetector filter Media Pipeline

WebRTC with plateDetector filter Media Pipeline

The complete source code of this demo can be found in GitHub.

This example is a modified version of the Magic Mirror tutorial. In this case, this demo uses a PlateDetector instead of FaceOverlay filter. An screenshot of the running example is shown in the following picture:

Plate detector demo in action

Plate detector demo in action

注解

Modules can have options. For configuring these options, you’ll need to get the constructor for them. In Javascript and Node, you have to use kurentoClient.getComplexType(‘qualifiedName’) . There is an example in the code.

The following snippet shows how the media pipeline is implemented in the Java server-side code of the demo. An important issue in this code is that a listener is added to the PlateDetectorFilter object (addPlateDetectedListener). This way, each time a plate is detected in the stream, a message is sent to the client side. As shown in the screenshot below, this event is printed in the console of the GUI.

...
kurento.register('kurento-module-platedetector');
...

function start(sessionId, ws, sdpOffer, callback) {
    if (!sessionId) {
        return callback('Cannot use undefined sessionId');
    }

    getKurentoClient(function(error, kurentoClient) {
        if (error) {
            return callback(error);
        }

        kurentoClient.create('MediaPipeline', function(error, pipeline) {
            if (error) {
                return callback(error);
            }

            createMediaElements(pipeline, ws, function(error, webRtcEndpoint, filter) {
                if (error) {
                    pipeline.release();
                    return callback(error);
                }

                if (candidatesQueue[sessionId]) {
                    while(candidatesQueue[sessionId].length) {
                        var candidate = candidatesQueue[sessionId].shift();
                        webRtcEndpoint.addIceCandidate(candidate);
                    }
                }

                connectMediaElements(webRtcEndpoint, filter, function(error) {
                    if (error) {
                        pipeline.release();
                        return callback(error);
                    }

                    webRtcEndpoint.on('OnIceCandidate', function(event) {
                        var candidate = kurento.getComplexType('IceCandidate')(event.candidate);
                        ws.send(JSON.stringify({
                            id : 'iceCandidate',
                            candidate : candidate
                        }));
                    });

                    filter.on('PlateDetected', function (data){
                        return callback(null, 'plateDetected', data);
                    });

                    webRtcEndpoint.processOffer(sdpOffer, function(error, sdpAnswer) {
                        if (error) {
                            pipeline.release();
                            return callback(error);
                        }

                        sessions[sessionId] = {
                            'pipeline' : pipeline,
                            'webRtcEndpoint' : webRtcEndpoint
                        }
                        return callback(null, 'sdpAnswer', sdpAnswer);
                    });

                    webRtcEndpoint.gatherCandidates(function(error) {
                        if (error) {
                            return callback(error);
                        }
                    });
                });
            });
        });
    });
}

function createMediaElements(pipeline, ws, callback) {
    pipeline.create('WebRtcEndpoint', function(error, webRtcEndpoint) {
        if (error) {
            return callback(error);
        }

        pipeline.create('platedetector.PlateDetectorFilter', function(error, filter) {
            if (error) {
                return callback(error);
            }

            return callback(null, webRtcEndpoint, filter);
        });
    });
}
Dependencies

Dependencies of this demo are managed using NPM. Our main dependency is the Kurento Client JavaScript (kurento-client). The relevant part of the package.json file for managing this dependency is:

"dependencies": {
   "kurento-client" : "6.6.0"
}

At the client side, dependencies are managed using Bower. Take a look to the bower.json file and pay attention to the following section:

"dependencies": {
   "kurento-utils" : "6.6.2",
   "kurento-module-pointerdetector": "6.6.0"
}

注解

We are in active development. You can find the latest versions at npm and Bower.

WebRTC Statistics

WebRTC Statistics

Introduction

WebRTC streams (audio, video, or data) can be lost, and experience varying amounts of network delay. In order to assess the performance of WebRTC applications, it could be required to be able to monitor the WebRTC features of the underlying network and media pipeline.

To that aim, Kurento provides WebRTC statistics gathering for the server-side (Kurento Media Server, KMS). The implementation of this capability follows the guidelines provided in the W3C WebRTC’s Statistics API. Therefore, the statistics gathered in the KMS can be divided into two groups:

  • inboundrtp: statistics on the stream received in the KMS.
  • outboundrtp: statistics on the stream sent by KMS.
API description

As usual, WebRTC statistics gathering capability is provided by the KMS and is consumed by means of the different Kurento client implementations (Java, JavaScript clients are provided out of the box). To read these statistics, first it should be enabled using the method setLatencyStats of a Media Pipeline object. Using the Kurento Java client this is done as follows:

String kmsWsUri = "ws://localhost:8888/kurento";
KurentoClient kurentoClient = KurentoClient.create(kmsWsUri);
MediaPipeline mediaPipeline = kurentoClient.createMediaPipeline();
mediaPipeline.setLatencyStats(true);

// ...

... and using the JavaScript client:

var kmsWsUri = "ws://localhost:8888/kurento";
kurentoClient(kmsWsUri, function(error, kurentoClient) {
   kurentoClient.create("MediaPipeline", function(error, mediaPipeline) {
      mediaPipeline.setLatencyStats(true, function(error){

         // ...

      });
   });
});

Once WebRTC statistics are enabled, the second step is reading the statistics values using the method getStats of a Media Element, For example, to read the statistics of a WebRtcEndpoint object in Java:

WebRtcEndpoint webRtcEndpoint = new WebRtcEndpoint.Builder(mediaPipeline).build();
MediaType mediaType = ... // it can be MediaType.VIDEO, MediaType.AUDIO, or MediaType.DATA
Map<String, Stats> statsMap = webRtcEndpoint.getStats(mediaType);

// ...

... and in JavaScript:

mediaPipeline.create("WebRtcEndpoint", function(error, webRtcEndpoint) {
   var mediaType = ... // it can be 'VIDEO', 'AUDIO', or 'DATA'
   webRtcEndpoint.getStats(mediaType, function(error, statsMap) {

      // ...

   });
});

Notice that the WebRTC statistics are read as a map. Therefore, each entry of this collection has a key and a value, in which the key is the specific statistic, with a given value at the reading time. Take into account that these values make reference to real-time properties, and so these values vary in time depending on multiple factors (for instance network performance, KMS load, and so on). The complete description of the statistics are defined in the KMD interface description. The most relevant statistics are listed below:

  • ssrc: The synchronized source (SSRC).
  • firCount: Count the total number of Full Intra Request (FIR) packets received by the sender. This metric is only valid for video and is sent by receiver.
  • pliCount: Count the total number of Packet Loss Indication (PLI) packets received by the sender and is sent by receiver.
  • nackCount: Count the total number of Negative ACKnowledgement (NACK) packets received by the sender and is sent by receiver.
  • sliCount: Count the total number of Slice Loss Indication (SLI) packets received by the sender. This metric is only valid for video and is sent by receiver.
  • remb: The Receiver Estimated Maximum Bitrate (REMB). This metric is only valid for video.
  • packetsLost: Total number of RTP packets lost for this SSRC.
  • packetsReceived: Total number of RTP packets received for this SSRC.
  • bytesReceived: Total number of bytes received for this SSRC.
  • jitter: Packet Jitter measured in seconds for this SSRC.
  • packetsSent: Total number of RTP packets sent for this SSRC.
  • bytesSent: Total number of bytes sent for this SSRC.
  • targetBitrate: Presently configured bitrate target of this SSRC, in bits per second.
  • roundTripTime: Estimated round trip time (seconds) for this SSRC based on the RTCP timestamp.
  • audioE2ELatency: End-to-end audio latency measured in nano seconds.
  • videoE2ELatency: End-to-end video latency measured in nano seconds.

All in all, the process for gathering WebRTC statistics in the KMS can be summarized in two steps: 1) Enable WebRTC statistics; 2) Read WebRTC. This process is illustrated in the following picture. This diagram also describes the JSON-RPC messages exchanged between Kurento client and KMS following the Kurento Protocol:

Sequence diagram for gathering WebRTC statistics in KMS

Sequence diagram for gathering WebRTC statistics in KMS

Example

There is a running tutorial which uses the WebRTC gathering as described before. This demo has been implemented using the JavaScript client and it is available on GitHub: kurento-loopback-stats.

From a the Media Pipeline point of view, this demo application consists in a WebRtcEndpoint in loopback. Once the demo is up and running, WebRTC are enabled and gathered with a rate of 1 second.

In addition to the KMS WebRTC statistics, the client-side (i.e. browser WebRtc peer) are also gathered by the application. This is done using the standard method provided by the peerConnection object, i.e using its method getStats. Please check out the JavaScript logic located in the index.js file for implementation details.

Both kinds of WebRTC statistics values (i.e. browser and KMS side) are updated and shown each second in the application GUI, as follows:

Statistics results in the kurento-loopback-stats demo GUI

Statistics results in the kurento-loopback-stats demo GUI

Kurento Utils JS

Kurento Utils JS

Overview

Kurento Utils is a wrapper object of an RTCPeerConnection. This object is aimed to simplify the development of WebRTC-based applications.

The source code of this project can be cloned from the GitHub repository.

How to use it

  • Minified file - Download the file from here.

  • NPM - Install and use library in your NodeJS files.

    npm install kurento-utils

    var utils = require('kurento-utils');

  • Bower - Generate the bundled script file

    bower install kurento-utils

    Import the library in your html page

    <script
src="bower_components/kurento-utils/js/kurento-utils.js"></script>
Examples

There are several tutorials that show kurento-utils used in complete WebRTC applications developed on Java, Node and JavaScript. These tutorials are in GitHub, and you can download and run them at any time.

In the following lines we will show how to use the library to create an RTCPeerConnection, and how to negotiate the connection with another peer. The library offers a WebRtcPeer object, which is a wrapper of the browser’s RTCPeerConnection API. Peer connections can be of different types: unidirectional (send or receive only) or bidirectional (send and receive). The following code shows how to create the latter, in order to be able to send and receive media (audio and video). The code assumes that there are two video tags in the page that loads the script. These tags will be used to show the video as captured by your own client browser, and the media received from the other peer. The constructor receives a property that holds all the information needed for the configuration.

 var videoInput = document.getElementById('videoInput');
 var videoOutput = document.getElementById('videoOutput');

 var constraints = {
     audio: true,
     video: {
       width: 640,
       framerate: 15
     }
 };

 var options = {
   localVideo: videoInput,
   remoteVideo: videoOutput,
   onicecandidate : onIceCandidate,
   mediaConstraints: constraints
 };


var webRtcPeer = kurentoUtils.WebRtcPeer.WebRtcPeerSendrecv(options, function(error) {
      if(error) return onError(error)

      this.generateOffer(onOffer)
   });

With this little code, the library takes care of creating the RTCPeerConnection, and invoking getUserMedia in the browser if needed. The constraints in the property are used in the invocation, and in this case both microphone and webcam will be used. However, this does not create the connection. This is only achieved after completing the SDP negotiation between peers. This process implies exchanging SDPs offer and answer and, since Trickle ICE is used, a number of candidates describing the capabilities of each peer. How the negotiation works is out of the scope of this document. More info can be found in this link.

In the previous piece of code, when the webRtcPeer object gets created, the SDP offer is generated with this.generateOffer(onOffer). The only argument passed is a function, that will be invoked one the browser’s peer connection has generated that offer. The onOffer callback method is responsible for sending this offer to the other peer, by any means devised in your application. Since that is part of the signaling plane and business logic of each particular application, it won’t be covered in this document.

Assuming that the SDP offer has been received by the remote peer, it must have generated an SDP answer, that should be received in return. This answer must be processed by the webRtcEndpoint, in order to fulfill the negotiation. This could be the implementation of the onOffer callback function. We’ve assumed that there’s a function somewhere in the scope, that allows sending the SDP to the remote peer.

function onOffer(error, sdpOffer) {
  if (error) return onError(error);

  // We've made this function up sendOfferToRemotePeer(sdpOffer,
  function(sdpAnswer) {
    webRtcPeer.processAnswer(sdpAnswer);
  });
}

As we’ve commented before, the library assumes the use of Trickle ICE to complete the connection between both peers. In the configuration of the webRtcPeer, there is a reference to a onIceCandidate callback function. The library will use this function to send ICE candidates to the remote peer. Since this is particular to each application, we will just show the signature

function onIceCandidate(candidate) {
  // Send the candidate to the remote peer
}

In turn, our client application must be able to receive ICE candidates from the remote peer. Assuming the signaling takes care of receiving those candidates, it is enough to invoke the following method in the webRtcPeer to consider the ICE candidate

webRtcPeer.addIceCandidate(candidate);

Following the previous steps, we have:

  • Sent and SDP offer to a remote peer
  • Received an SDP answer from the remote peer, and have the webRtcPeer process that answer.
  • Exchanged ICE candidates between both peer, by sending the ones generated in the browser, and processing the candidates received by the remote peer.

This should complete the negotiation process, and should leave us with a working bidirectional WebRTC media exchange between both peers.

Using data channels

WebRTC data channels lets you send text or binary data over an active WebRTC connection. The WebRtcPeer object can provide access to this functionality by using the RTCDataChannel form the wrapped RTCPeerConnection object. This allows you to inject into and consume data from the pipeline. This data can be treated by each endpoint differently. For instance, a WebRtcPeer object in the browser, will have the same behavior as the RTCDataChannel (you can see a description here). Other endpoints could make use of this channel to send information: a filter that detects QR codes in a video stream, could send the detected code to the clients through a data channel. This special behavior should be specified in the filter.

The use of data channels in the WebRtcPeer object is indicated by passing the dataChannels flag in the options bag, along with the desired options.

 var options = {
     localVideo : videoInput,
     remoteVideo : videoOutput,
     dataChannels : true,
     dataChannelConfig: {
       id : getChannelName(),
       onmessage : onMessage,
       onopen : onOpen,
       onclose : onClosed,
       onbufferedamountlow : onbufferedamountlow,
       onerror : onerror
     },
     onicecandidate : onIceCandidate
 }

 webRtcPeer = new kurentoUtils.WebRtcPeer.WebRtcPeerSendrecv(options, onWebRtcPeerCreated);

The values in dataChannelConfig are all optional. Once the webRtcPeer object is created, and after the connection has been successfully negotiated, users can send data through the data channel

webRtcPeer.send('your data stream here');

The format of the data you are sending, is determined by your application, and the definition of the endpoints that you are using.

The lifecycle of the underlying RTCDataChannel, is tied to that of the webRtcPeer: when the webRtcPeer.dispose() method is invoked, the data channel will be closed and released too.

Reference documentation
WebRtcPeer

The constructor for WebRtcPeer is WebRtcPeer(mode, options, callback) where:

  • mode: Mode in which the PeerConnection will be configured. Valid values are

    • recv: receive only media.
    • send: send only media.
    • sendRecv: send and receive media.

  • options : It is a group of parameters and they are optional. It is a json object.

    • localVideo: Video tag in the application for the local stream.

    • remoteVideo: Video tag in the application for the remote stream.

    • videoStream: Provides an already available video stream that will be used instead of using the media stream from the local webcam.

    • audioStreams: Provides an already available audio stream that will be used instead of using the media stream from the local microphone.

    • mediaConstraints: Defined the quality for the video and audio

    • connectionConstraints: Defined the connection constraint according with browser like googIPv6, DtlsSrtpKeyAgreement...

    • peerConnection: Use a peerConnection which was created before

    • sendSource: Which source will be used

      • webcam
      • screen
      • window

    • onstreamended: Method that will be invoked when stream ended event happens

    • onicecandidate: Method that will be invoked when ice candidate event happens

    • oncandidategatheringdone: Method that will be invoked when all candidates have been harvested

    • dataChannels: Flag for enabling the use of data channels. If true, then a data channel will be created in the RTCPeerConnection object.

    • dataChannelConfig: It is a JSON object with the configuration passed to the DataChannel when created. It supports the following keys:

      • id: Specifies the id of the data channel. If none specified, the same id of the WebRtcPeer object will be used.
      • options: Options object passed to the data channel constructor.
      • onopen: Function invoked in the onopen event of the data channel, fired when the channel is open.
      • onclose: Function invoked in the onclose event of the data channel, fired when the data channel is closed.
      • onmessage: Function invoked in the onmessage event of the data channel. This event is fired every time a message is received.
      • onbufferedamountlow: Is the event handler called when the bufferedamountlow event is received. Such an event is sent when RTCDataChannel.bufferedAmount drops to less than or equal to the amount specified by the RTCDataChannel.bufferedAmountLowThreshold property.
      • onerror: Callback function onviked when an error in the data channel is produced. If none is provided, an error trace message will be logged in the browser console.

    • simulcast: Indicates whether simulcast is going to be used. Value is true|false

    • configuration: It is a JSON object where ICE Servers are defined using

      • iceServers: The format for this variable is like:

        [{"urls":"turn:turn.example.org","username":"user","credential":"myPassword"}]
[{"urls":"stun:stun1.example.net"},{"urls":"stun:stun2.example.net"}]

  • callback: It is a callback function which indicate, if all worked right or not

Also there are 3 specific methods for creating WebRtcPeer objects without using mode parameter:

  • WebRtcPeerRecvonly(options, callback): Create a WebRtcPeer as receive only.
  • WebRtcPeerSendonly(options, callback): Create a WebRtcPeer as send only.
  • WebRtcPeerSendrecv(options, callback): Create a WebRtcPeer as send and receive.
MediaConstraints

Constraints provide a general control surface that allows applications to both select an appropriate source for a track and, once selected, to influence how a source operates. getUserMedia() uses constraints to help select an appropriate source for a track and configure it. For more information about media constraints and its values, you can check here.

By default, if the mediaConstraints is undefined, this constraints are used when getUserMedia is called:

{
  audio: true,
  video: {
    width: 640,
    framerate: 15
  }
}

If mediaConstraints has any value, the library uses this value for the invocation of getUserMedia. It is up to the browser whether those constraints are accepted or not.

In the examples section, there is one example about the use of media constraints.

Methods
getPeerConnection

Using this method the user can get the peerConnection and use it directly.

showLocalVideo

Use this method for showing the local video.

getLocalStream

Using this method the user can get the local stream. You can use muted property to silence the audio, if this property is true.

getRemoteStream

Using this method the user can get the remote stream.

getCurrentFrame

Using this method the user can get the current frame and get a canvas with an image of the current frame.

processAnswer

Callback function invoked when a SDP answer is received. Developers are expected to invoke this function in order to complete the SDP negotiation. This method has two parameters:

  • sdpAnswer: Description of sdpAnswer
  • callback: It is a function with error like parameter. It is called when the remote description has been set successfully.
processOffer

Callback function invoked when a SDP offer is received. Developers are expected to invoke this function in order to complete the SDP negotiation. This method has two parameters:

  • sdpOffer: Description of sdpOffer
  • callback: It is a function with error and sdpAnswer like parameters. It is called when the remote description has been set successfully.
dispose

This method frees the resources used by WebRtcPeer.

addIceCandidate

Callback function invoked when an ICE candidate is received. Developers are expected to invoke this function in order to complete the SDP negotiation. This method has two parameters:

  • iceCandidate: Literal object with the ICE candidate description
  • callback: It is a function with error like parameter. It is called when the ICE candidate has been added.
getLocalSessionDescriptor

Using this method the user can get peerconnection’s local session descriptor.

getRemoteSessionDescriptor

Using this method the user can get peerconnection’s remote session descriptor.

generateOffer

Creates an offer that is a request to find a remote peer with a specific configuration.

How to do screen share

Screen and window sharing depends on the privative module kurento-browser-extensions. To enable its support, you’ll need to install the package dependency manually or provide a getScreenConstraints function yourself on runtime. The option sendSource could be window or screen before create a WebRtcEndpoint. If it’s not available, when trying to share the screen or a window content it will throw an exception.

Souce code

The code is at github.

Be sure to have Node.js and Bower installed in your system:

curl -sL https://deb.nodesource.com/setup_4.x | sudo bash -
sudo apt-get install -y nodejs
sudo npm install -g bower

To install the library, it is recommended to do that from the NPM repository:

npm install kurento-utils

Alternatively, you can download the code using Git and install manually its dependencies:

git clone https://github.com/Kurento/kurento-utils
cd kurento-utils
npm install
Build for browser

After you download the project, to build the browser version of the library you’ll only need to execute the grunt task runner. The file needed will be generated on the dist folder. Alternatively, if you don’t have it globally installed, you can run a local copy by executing:

cd kurento-utils
node_modules/.bin/grunt

Kurento Java Client JavaDoc

Kurento JavaScript Client JsDoc

Kurento JavaScript Utils JsDoc

Securing Kurento Applications

Securing Kurento Applications

Starting with Chrome 47, WebRTC is only allowed from SECURE ORIGINS (HTTPS or localhost). Check their release notes for further information about this issue.

注解

Keep in mind that serving your application through HTTPS, forces you to use WebSockets Secure (WSS) if you are using websockets to control your application server.

Securing client applications
Configure Java applications to use HTTPS

  • The application needs a certificate in order to enable HTTPS:

    • Request a certificate from a local certification authority.

    • Create an self-signed certificate.

      keytool -genkey -keyalg RSA -alias selfsigned -keystore \
keystore.jks -storepass password -validity 360 -keysize 2048

  • Use the certificate in your application:

    • Include a valid keystore in the jar file:

      File keystore.jks must be in the project’s root path, and a file named application.properties must exist in src/main/resources/, with the following content:

      server.port: 8443
server.ssl.key-store: keystore.jks
server.ssl.key-store-password: yourPassword
server.ssl.keyStoreType: JKS
server.ssl.keyAlias: yourKeyAlias
    • You can also specify the location of the properties file. When launching your Spring-Boot based app, issue the flag -Dspring.config.location=<path-to-properties> .

  • Start application

mvn compile exec:java -Dkms.url=ws://kms_host:kms_port/kurento

注解

If you plan on using a webserver as proxy, like Nginx or Apache, you’ll need to setAllowedOrigins when registering the handler. Please read the official Spring documentation entry for more info.

Configure Node applications to use HTTPS

  • The application requires a valid SSL certificate in order to enable HTTPS:

    • Request a certificate from a local certification authority.
    • Create your own self-signed certificate as explained here. This will show you how to create the required files: server.crt, server.key and server.csr.

Add the following changes to server.js in order to enable HTTPS:

...
var express = require('express');
var ws = require('ws');
var fs    = require('fs');
var https = require('https');
...

var options =
{
  key:  fs.readFileSync('key/server.key'),
  cert: fs.readFileSync('keys/server.crt')
};

var app = express();

var server = https.createServer(options, app).listen(port, function() {
...
});
...

var wss = new ws.Server({
 server : server,
 path : '/'
});

wss.on('connection', function(ws) {

....
  • Start application
npm start
Configure Javascript applications to use HTTPS

  • You’ll need to provide a valid SSL certificate in order to enable HTTPS:

    • Request a certificate from a local certification authority.
    • Create your own self-signed certificate as explained here. This will show you how to create the required files: server.crt, server.key and server.csr.

  • Start the application using the certificates:

http-server -p 8443 -S -C keys/server.crt -K keys/server.key
Securing server applications
Configure Kurento Media Server to use Secure WebSocket (WSS)

First, you need to change the configuration file of Kurento Media Server, i.e. /etc/kurento/kurento.conf.json, uncommenting the following lines:

"secure": {
  "port": 8433,
  "certificate": "defaultCertificate.pem",
  "password": ""
},

If this PEM certificate is a signed certificate (by a Certificate Authority such as Verisign), then you are done. If you are going to use a self-signed certificate (suitable for development), then there is still more work to do.

You can generate a self signed certificate by doing this:

certtool --generate-privkey --outfile defaultCertificate.pem
echo 'organization = your organization name' > certtool.tmpl
certtool --generate-self-signed --load-privkey defaultCertificate.pem \
   --template certtool.tmpl >> defaultCertificate.pem
sudo chown kurento defaultCertificate.pem

Due to the fact that the certificate is self-signed, applications will reject it by default. For this reason, you’ll need to force them to accept it.

  • Browser applications: You’ll need to manually accept the certificate as trusted one before secure WebSocket connections can be established. By default, this can be done by connecting to connecting to https://localhost:8433/kurento and accepting the certificate in the browser.
  • Java applications, follow the instructions of this link (get InstallCert.java from here). You’ll need to instruct the KurentoClient needs to be configured to allow the use of certificates. For this purpose, we need to create our own JsonRpcClient:
SslContextFactory sec = new SslContextFactory(true);
sec.setValidateCerts(false);
JsonRpcClientWebSocket rpcClient = new JsonRpcClientWebSocket(uri, sec);
KurentoClient kuretoClient = KurentoClient.createFromJsonRpcClient(rpcClient);
  • Node applications, please take a look to this page.

Second, you have to change the WebSocket URI in your application logic. For instance, in the hello-world application within the tutorials, this would be done as follows:

  • Java: Changing this line in HelloWorldApp.java:

    final static String DEFAULT_KMS_WS_URI = "wss://localhost:8433/kurento";

  • Browser JavaScript: Changing this line in index.js:

    const ws_uri = 'wss://' + location.hostname + ':8433/kurento';

  • Node.js: Changing this line in server.js:

    const ws_uri = "wss://localhost:8433/kurento";

Kurento FAQ

This is a list of Frequently Asked Questions about Kurento. Feel free to suggest new entries or different wording for answers!

How do I...

...install Kurento Media Server in an Amazon EC2 instance?

If you are installing Kurento in a NAT environment (i.e. in any cloud provider), you’ll need to provide a STUN server configuration in /etc/kurento/modules/kurento/WebRtcEndpoint.conf.ini. Apart from that, you will have to open all UDP ports in your security group, as STUN will use any port available from the whole 0-65535 range.

Though for most situations it’s enough to configure a STUN server in the KMS configuration files, you might need to install a TURN server, for example coturn. Here are some instructions on how to install this TURN server for Kurento:

1. Download the package from the project’s page.

2. Extract the contents. You should have a INSTALL file with instructions, and a .deb package. Follow the instructions to install the package.

3. Once the package is installed, you’ll need to modify the startup script in /etc/init.d/coturn.

  • Add the external and local IPs as vars:

    EXTERNAL_IP=$(curl http://169.254.169.254/latest/meta-data/public-ipv4)
LOCAL_IP=$(curl http://169.254.169.254/latest/meta-data/local-ipv4)

  • Modify the DAEMON_ARGS var to take these IPs into account, along with the long-term credentials user and password (kurento:kurento in this case, but could be different), realm and some other options:

    DAEMON_ARGS="-c /etc/turnserver.conf -f -o -a -v -r kurento.org
-u kurento:kurento --no-stdout-log --external-ip $EXTERNAL_IP/$LOCAL_IP"

4. Then let’s enable the turnserver to run as an automatic service daemon. For this, open the file /etc/default/coturn and uncomment the key:

TURNSERVER_ENABLED=1

5. Now, you have to tell the Kurento server where is the turnserver installed. For this, modify the turnURL key in /etc/kurento/modules/kurento/WebRtcEndpoint.conf.ini:

turnURL=kurento:kurento@<public-ip>:3478
stunServerAddress=<public-ip>
stunServerPort=3478

The following ports should be open in the firewall:

  • 3478 TCP & UDP
  • 49152 - 65535 UDP: As per RFC 5766, these are the ports that the TURN server will use to exchange media. These ports can be changed using the --max-port and --min-port options from the turnserver.

注解

While the RFC specifies the ports used by TURN, if you are using STUN you will need to open all UDP ports, as those ports are not constrained.

6. The last thing to do, is to start the coturn server and the media server:

sudo service coturn start && sudo service kurento-media-server-6.0 restart

注解

Please do make sure you check your installation using this test application

...know how many Media Pipelines do I need for my Application?

Media Elements can only communicate with each other when they are part of the same pipeline. Different MediaPipelines in the server are independent do not share audio, video, data or events.

A good heuristic is that you will need one pipeline per each set of communicating partners in a channel, and one Endpoint in this pipeline per audio/video streams reaching a partner.

...know how many Endpoints do I need?

Your application will need to create an Endpoint for each media stream flowing to (or from) the pipeline. As we said in the previous answer, each set of communicating partners in a channel will be in the same Media Pipeline, and each of them will use one or more Endpoints. They could use more than one if they are recording or reproducing several streams.

...know to what client a given WebRtcEndPoint belongs or where is it coming from?

Kurento API currently offers no way to get application attributes stored in a Media Element. However, the application developer can maintain a hashmap or equivalent data structure mapping the WebRtcEndpoint internal Id (which is a string) to whatever application information is desired.

Why do I get the error...

...”Cannot create gstreamer element”?

This is a typical error which happens when you update Kurento Media Server from version 4 to 5. The problem is related to the GStreamer dependency version. The solution is the following:

sudo apt-get remove kurento*
sudo apt-get autoremove
sudo apt-get update
sudo apt-get dist-upgrade
sudo apt-get install kurento-media-server-6.0

术语表

This is a glossary of terms that often appear in discussion about multimedia transmissions. Most of the terms are described and linked to its wikipedia, RFC or W3C relevant documents. Some of the terms are specific to gstreamer or kurento.

Agnostic, Media
One of the big problems of media is that the number of variants of video and audio codecs, formats and variants quickly creates high complexity in heterogeneous applications. So kurento developed the concept of an automatic converter of media formats that enables development of agnostic elements. Whenever a media element’s source is connected to another media element’s sink, the kurento framework verifies if media adaption and transcoding is necessary and, if needed, it transparently incorporates the appropriate transformations making possible the chaining of the two elements into the resulting Pipeline.
AVI

Audio Video Interleaved, known by its initials AVI, is a multimedia container format introduced by Microsoft in November 1992 as part of its Video for Windows technology. AVI files can contain both audio and video data in a file container that allows synchronous audio-with-video playback. AVI is a derivative of the Resource Interchange File Format (RIFF).

参见

Audio Video Interleave
Wikipedia reference of the AVI format
Resource Interchange File Format
Wikipedia reference of the RIFF format
Bower
Bower is a package manager for the web. It offers a generic solution to the problem of front-end package management, while exposing the package dependency model via an API that can be consumed by a build stack.
Builder Pattern

The builder pattern is an object creation software design pattern whose intention is to find a solution to the telescoping constructor anti-pattern. The telescoping constructor anti-pattern occurs when the increase of object constructor parameter combination leads to an exponential list of constructors. Instead of using numerous constructors, the builder pattern uses another object, a builder, that receives each initialization parameter step by step and then returns the resulting constructed object at once.

参见

Builder_pattern
Wikipedia reference of the Builder Pattern
CORS

CORS is a mechanism that allows JavaScript code on a web page to make XMLHttpRequests to different domains than the one the JavaScript originated from. It works by adding new HTTP headers that allow servers to serve resources to permitted origin domains. Browsers support these headers and enforce the restrictions they establish.

参见

enable-cors.org
for information on the relevance of CORS and how and when to enable it.
DOM
Document Object Model
Document Object Model is a cross-platform and language-independent convention for representing and interacting with objects in HTML, XHTML and XML documents.
EOS
Acronym of End Of Stream. In Kurento some elements will raise an EndOfStream event when the media they are processing is finished.
GStreamer
GStreamer is a pipeline-based multimedia framework written in the C programming language.
H.264

A Video Compression Format. The H.264 standard can be viewed as a “family of standards” composed of a number of profiles. Each specific decoder deals with at least one such profiles, but not necessarily all. See H.264 entry at wikipedia

参见

RFC 6184
RTP Payload Format for H.264 Video. This RFC obsoletes RFC 3984.
HTTP

The Hypertext Transfer Protocol is an application protocol for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web.

参见

RFC 2616

ICE
Interactive Connectivity Establishment

Interactive Connectivity Establishment (ICE) is a technique used to achieve NAT Traversal. ICE makes use of the STUN protocol and its extension, TURN. ICE can be used by any protocol utilizing the offer/answer model.

参见

RFC 5245

Interactive Connectivity Establishment
Wikipedia reference of ICE
IMS

IP Multimedia Subsystem is 3GPP Mobile Architectural Framework for delivering IP Multimedia Services in 3G (and beyond) Mobile Networks.

参见

RFC 3574

Java EE

Java EE, or Java Platform, Enterprise Edition, is a standardised set of APIs for Enterprise software development.

参见

Oracle Site
Java EE Overview
Wikipedia
Java Platform Enterprise Edition
jQuery
jQuery is a cross-platform JavaScript library designed to simplify the client-side scripting of HTML.
JSON
JSON (JavaScript Object Notation) is a lightweight data-interchange format. It is designed to be easy to understand and write for humans and easy to parse for machines.
JSON-RPC
JSON-RPC is a simple remote procedure call protocol encoded in JSON. JSON-RPC allows for notifications and for multiple calls to be sent to the server which may be answered out of order.
Kurento
Kurento is a platform for the development of multimedia enabled applications. Kurento is the Esperanto term for the English word ‘stream’. We chose this name because we believe the Esperanto principles are inspiring for what the multimedia community needs: simplicity, openness and universality. Kurento is open source, released under Apache 2.0, and has several components, providing solutions to most multimedia common services requirements. Those components include: Kurento Media Server, Kurento API, Kurento Protocol, and Kurento Client.
Kurento API
Kurento API is an object oriented API to create media pipelines to control media. It can be seen as and interface to Kurento Media Server. It can be used from the Kurento Protocol or from Kurento Clients.
Kurento Client
A Kurento Client is a programming library (Java or JavaScript) used to control Kurento Media Server from an application. For example, with this library, any developer can create a web application that uses Kurento Media Server to receive audio and video from the user web browser, process it and send it back again over Internet. Kurento Client exposes the Kurento API to app developers.
Kurento Protocol
Communication between KMS and clients by means of JSON-RPC messages. It is based on WebSocket that uses JSON-RPC V2.0 messages for making requests and sending responses.
Kurento Media Server
Kurento Media Server is the core element of Kurento since it responsible for media transmission, processing, loading and recording.
Maven
Maven is a build automation tool used primarily for Java projects.
Media Element
A Media Element is a module that encapsulates a specific media capability. For example RecorderEndpoint, PlayerEndpoint, etc.
Media Pipeline
A Media Pipeline is a chain of media elements, where the output stream generated by one element (source) is fed into one or more other elements input streams (sinks). Hence, the pipeline represents a “machine” capable of performing a sequence of operations over a stream.
Media Plane

In the traditional 3GPP Mobile Carrier Media Framework, the handling of media is conceptually splitted in two layers. The one that handles the media itself, with functionalities such as media transport, encoding/decoding, and processing, is called Media Plane.

参见

Signaling Plane

MP4

MPEG-4 Part 14 or MP4 is a digital multimedia format most commonly used to store video and audio, but can also be used to store other data such as subtitles and still images.

参见

Wikipedia definition of MP4.

Multimedia

Multimedia is concerned with the computer controlled integration of text, graphics, video, animation, audio, and any other media where information can be represented, stored, transmitted and processed digitally.

There is a temporal relationship between many forms of media, for instance audio, video and animations. There 2 are forms of problems involved in

  • Sequencing within the media, i.e. playing frames in correct order or time frame.
  • Synchronisation, i.e. inter-media scheduling. For example, keeping video and audio synchronized or displaying captions or subtitles in the required intervals.

参见

Wikipedia definition of Multimedia

Multimedia container format

Container or wrapper formats are metafile formats whose specification describes how different data elements and metadata coexist in a computer file.

Simpler multimedia container formats can contain different types of audio formats, while more advanced container formats can support multiple audio and video streams, subtitles, chapter-information, and meta-data, along with the synchronization information needed to play back the various streams together. In most cases, the file header, most of the metadata and the synchro chunks are specified by the container format.

参见

Wikipedia definition of multimedia container formats

NAT
Network Address Translation

Network address translation (NAT) is the technique of modifying network address information in Internet Protocol (IP) datagram packet headers while they are in transit across a traffic routing device for the purpose of remapping one IP address space into another.

参见

Network Address Translation definition at Wikipedia

NAT-T
NAT Traversal

NAT traversal (sometimes abbreviated as NAT-T) is a general term for techniques that establish and maintain Internet protocol connections traversing network address translation (NAT) gateways, which break end-to-end connectivity. Intercepting and modifying traffic can only be performed transparently in the absence of secure encryption and authentication.

参见

NAT Traversal White Paper
White paper on NAT-T and solutions for end-to-end connectivity in its presence
Node.js
Node.js is a cross-platform runtime environment for server-side and networking applications. Node.js applications are written in JavaScript, and can be run within the Node.js runtime on OS X, Microsoft Windows and Linux with no changes.
npm
npm is the official package manager for Node.js.
OpenCL
OpenCL™ is standard framework for cross-platform, parallel programming of heterogeneous platforms consisting of central processing units (CPUs), graphics processing units (GPUs), digital signal processors (DSPs), field-programmable gate arrays (FPGAs) and other processors.
OpenCV
OpenCV (Open Source Computer Vision Library) is a BSD-licensed open source computer vision and machine learning software library. OpenCV aims to provide a common infrastructure for computer vision applications and to accelerate the use of machine perception.
Pad, Media

A Media Pad is is an element´s interface with the outside world. Data streams from the MediaSource pad to another element’s MediaSink pad.

参见

GStreamer Pad
Definition of the Pad structure in GStreamer
PubNub
PubNub is a publish/subscribe cloud service for sending and routing data. It streams data to global audiences on any device using persistent socket connections. PubNub has been designed to deliver data with low latencies to end-user devices. These devices can be behind firewalls, NAT environments, and other hard-to-reach network environments. PubNub provides message caching for retransmission of lost signals over unreliable network environments. This is accomplished by maintaining an always open socket connection to every device.
QR

QR code (Quick Response Code) is a type of two-dimensional barcode. that became popular in the mobile phone industry due to its fast readability and greater storage capacity compared to standard UPC barcodes.

参见

QR Code
Entry in wikipedia
REST
Representational State Transfer is an architectural style consisting of a coordinated set of constraints applied to components, connectors, and data elements, within a distributed hypermedia system. The term representational state transfer was introduced and defined in 2000 by Roy Fielding in his doctoral dissertation.
RTCP

The RTP Control Protocol is a sister protocol of the RTP, that provides out-of-band statistics and control information for an RTP flow.

参见

RFC 3605

RTP

The Real-Time Transport Protocol is a standard packet format designed for transmitting audio and video streams on IP networks. It is used in conjunction with the RTP Control Protocol. Transmissions using the RTP audio/video profile typically use SDP to describe the technical parameters of the media streams.

参见

RFC 3550

Same-origin policy
The Same-origin policy is web application security model. The policy permits scripts running on pages originating from the same site to access each other’s DOM with no specific restrictions, but prevents access to DOM on different sites.
SDP
Session Description Protocol

The Session Description Protocol describes initialization parameters for a streaming media session. Both parties of a streaming media session exchange SDP files to negotiate and agree in the parameters to be used for the streaming.

参见

RFC 4566
Definition of Session Description Protocol
RFC 4568
Security Descriptions for Media Streams in SDP
Semantic Versioning
Semantic Versioning is a formal convention for specifying
compatibility using a three-part version number: major version; minor version; and patch.
Signaling Plane

It is the layer of a media system in charge of the information exchanges concerning the establishment and control of the different media circuits and the management of the network, in contrast to the transfer of media, done by the Signaling Plane.

Functions such as media negotiation, QoS parametrization, call establishment, user registration, user presence, etc. as managed in this plane.

参见

Media Plane

Sink, Media
A Media Sink is a MediaPad that outputs a Media Stream. Data streams from a MediaSource pad to another element’s MediaSink pad.
SIP

Session Initiation Protocol is a signaling plane protocol widely used for controlling multimedia communication sessions such as voice and video calls over Internet Protocol (IP) networks. SIP works in conjunction with several other application layer protocols:

  • SDP for media identification and negotiation
  • RTP, SRTP or WebRTC for the transmission of media streams
  • A TLS layer may be used for secure transmission of SIP messages
Source, Media
A Media Source is a Media Pad that generates a Media Stream.
SPA
Single-Page Application
A single-page application is a web application that fits on a single web page with the goal of providing a more fluid user experience akin to a desktop application.
Sphinx

Documentation generation system used for kurento documentation

参见

Easy and beautiful documentation with Sphinx

Spring Boot
Spring Boot is Spring’s convention-over-configuration solution for creating stand-alone, production-grade Spring based applications that can you can “just run”. It embeds Tomcat or Jetty directly and so there is no need to deploy WAR files in order to run web applications.
SRTCP

SRTCP provides the same security-related features to RTCP, as the ones provided by SRTP to RTP. Encryption, message authentication and integrity, and replay protection are the features added by SRTCP to RTCP.

参见

SRTP

SRTP
Secure RTP
is a profile of RTP (Real-time Transport Protocol), intended to provide encryption, message authentication and integrity, and replay protection to the RTP data in both unicast and multicast applications. Similar to how RTP has a sister RTCP protocol, SRTP also has a sister protocol, called Secure RTCP (or SRTCP);

参见

RFC 3711

SSL
Secure Socket Layer. See TLS.
STUN
Session Traversal Utilities for NAT
STUN is a standardized set of methods to allow an end host to discover its public IP address if it is located behind a NAT. STUN is a client-server protocol returning the public IP address to a client together with information from which the client can infer the type of NAT it sits behind.
Trickle ICE

Extension to the ICE protocol that allows ICE agents to send and receive candidates incrementally rather than exchanging complete lists. With such incremental provisioning, ICE agents can begin connectivity checks while they are still gathering candidates and considerably shorten the time necessary for ICE processing to complete.

参见

Trickle ICE IETF Draft

TLS

Transport Layer Security and its prececessor Secure Socket Layer (SSL)

参见

RFC 5246
Version 1.2 of the Transport Layer Security protocol
TURN
Traversal Using Relays around NAT
TURN is a protocol that allows for a client behind a NAT or firewall to receive incoming data over TCP or UDP connections. TURN places a third party server to relay messages between two clients where peer to peer media traffic is not allowed by a firewall.
VP8

VP8 is a video compression format created by On2 Technologies as a successor to VP7. Its patents rights are owned by Google, who made an irrevocable patent promise on its patents for implementing it and released a specification under the Creative Commons Attribution 3.0 license.

参见

RFC 6386
VP8 Data Format and Decoding Guide
VP8
VP8 page at Wikipedia
WebM
WebM is an open media file format designed for the web. WebM files consist of video streams compressed with the VP8 video codec and audio streams compressed with the Vorbis audio codec. The WebM file structure is based on the Matroska media container.
WebRTC

WebRTC is an open source project that provides rich Real-Time Communcations capabilities to web browsers via Javascript and HTML5 APIs and components. These APIs are being drafted by the World Wide Web Consortium (W3C).

参见

WebRTC Working Draft

WebSocket
WebSocket specification (developed as part of the HTML5 initiative) defines a full-duplex single socket connection over which messages can be sent between client and server.