In fact, while building the service for taking screenshots, we have done most of the work for screencast recording. We already have the MediaStream object delivered by webkitGetUserMedia. We just need a way to define the start and end of recording and save the collected frames in a video file. That is where we can benefit from the MediaStream Recording API, which captures the data produced by MedaStream or HTMLMediaElement (for example, <video>) so that we can save it. So, we modify the service again:

./js/Service/Capturer.js

//... 
const toBuffer = require( "blob-to-buffer" ); 
//... 
start( desktopStreamId ){ 
    navigator.webkitGetUserMedia(/* constaints */, ( stream ) => { 
        let chunks = []; 
        this.dom.video.srcObject = stream; 
        this.mediaRecorder = new MediaRecorder( stream ); 
        this.mediaRecorder.onstop = (...