Discover the new easier way to develop Kurento video applications

Node.js - WebRTC magic mirror

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

Note

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 6.9.0
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).

Note

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" : "6.9.0"
}

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" : "6.9.0"
}

Note

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