Warning

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.

Node.js Module - Chroma Filter

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

Note

Web browsers require using HTTPS to enable WebRTC, so the web server must use SSL and a certificate file. For instructions, check Configure a Node.js server to use HTTPS.

For convenience, this tutorial already provides dummy self-signed certificates (which will cause a security warning in the browser).

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 kurento-module-chroma should be also installed:

sudo apt-get install kurento-module-chroma

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

curl -sSL https://deb.nodesource.com/setup_18.x | sudo -E bash -
sudo apt-get install -y nodejs

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.git
cd kurento/tutorials/javascript-node/chroma/
git checkout main
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

Finally, access the application connecting to the URL https://localhost:8443/ through 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}:8888/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

Note

Modules can have options. For configuring these options, you’ll need to get the constructor for 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:

...
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('IceCandidateFound', 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" : "7.0.0"
}

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

Note

You can find the latest versions at npm and Bower.