Discover the new easier way to develop Kurento video applications

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.

Running this example

First of all, install Kurento Media Server: Installation Guide. Start the media server and leave it running in the background.

Install Node.js, Bower, and a web server in your system:

curl -sL | sudo -E bash -
sudo apt-get install -y nodejs
sudo npm install -g bower
sudo npm install -g http-server

Here, we suggest using the simple Node.js http-server, but you could use any other web server.

You also need the source code of this tutorial. Clone it from GitHub, then start the web server:

git clone
cd kurento-tutorial-js/kurento-hello-world-data-channel/
git checkout master
bower install
http-server -p 8443 --ssl --cert keys/server.crt --key keys/server.key

Note that HTTPS is required by browsers to enable WebRTC, so the web server must use SSL and a certificate file. For instructions, check Configure JavaScript applications to use HTTPS. For convenience, this tutorial already provides dummy self-signed certificates (which will cause a security warning in the browser).

When your web server is up and running, use a WebRTC compatible browser (Firefox, Chrome) to open the tutorial page:

  • If KMS is running in your local machine:

  • If KMS is running in a remote machine:



By default, this tutorial works out of the box by using non-secure WebSocket (ws://) to establish a client connection between the browser and KMS. This only works for localhost. It will fail if the web server is remote.

If you want to run this tutorial from a remote web server, then you have to do 3 things:

  1. Configure Secure WebSocket in KMS. For instructions, check Securing Kurento Media Server.
  2. In index.js, change the ws_uri to use Secure WebSocket (wss:// instead of ws://) and the correct KMS port (8433 instead of 8888).
  3. As explained in the link from step 1, if you configured KMS to use Secure WebSocket with a self-signed certificate you now have to browse to https://{KMS_HOST}:8433/kurento and click to accept the untrusted certificate.


This demo uses the kms-datachannelexample module, which must be installed in the media server. That module is available in the Kurento Apt repositories, so it is possible to install it with this command:

sudo apt-get update && sudo apt-get install --yes 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)


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(,
    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);


     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(){


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



Demo dependencies are defined in file bower.json. They are managed using Bower.

"dependencies": {
   "kurento-client": "6.14.0",
   "kurento-utils": "6.14.0"


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