Kurento is a low-level platform to create WebRTC applications from scratch. You will be responsible of managing STUN/TURN servers, networking, scalability, etc. If you are new to WebRTC, we recommend using OpenVidu instead.

OpenVidu is an easier to use, higher-level, Open Source platform based on Kurento.

JavaScript Module - Chroma Filter


Bower dependencies are not yet upgraded for Kurento 7.0.0.

Kurento tutorials that use pure browser JavaScript need to be rewritten to drop the deprecated Bower service and instead use a web resource packer. This has not been done, so these tutorials won’t be able to download the dependencies they need to work. PRs would be appreciated!

This web application consists of a WebRTC video communication in mirror (loopback) with a chroma filter element.


Web browsers require using HTTPS 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).

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 -sSL https://deb.nodesource.com/setup_18.x | 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 https://github.com/Kurento/kurento.git
cd kurento/tutorials/javascript-browser/chroma/
git checkout main
bower install
http-server -p 8443 --ssl --cert keys/server.crt --key keys/server.key

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 Signaling Plane security (WebSocket).

  2. In index.js, change the ws_uri to use Secure WebSocket (wss:// instead of ws://) and the correct KMS port (TCP 8433 instead of TCP 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.


By default, this tutorial assumes that Kurento Media Server can download the overlay image from a localhost web server. It will fail if the web server is remote (from the point of view of KMS). This includes the case of running KMS from Docker.

If you want to run this tutorial with a remote Kurento Media Server (including running KMS from Docker), then you have to provide it with the correct IP address of the application’s web server:

  • In index.js, change bg_uri to the correct one where KMS can reach the web server.

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


Modules can have options. For configure these options, you need get the constructor to them. In JavaScript and Node.js, 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:

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...");


      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");


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



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": "7.0.0",
   "kurento-utils": "7.0.0"
   "kurento-module-pointerdetector": "7.0.0"

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

bower install


You can find the latest versions at Bower.