894556 - Multiple video tracks in a MediaStream are not reflected on the videoTracks object on the video element

Le premier numéro que j'ai trouvé en essayant de créer un éditeur de vidéo sur le Web.

J'ai plusieurs flux vidéo (ordinateur de bureau et webcam) et je voulais pouvoir basculer entre les flux vidéo sur un élément vidéo afin de pouvoir basculer rapidement entre la webcam et le bureau et ne pas casser le MediaRecorder.

Il semble que vous devriez pouvoir le faire en basculant la propriété selected sur l'objet videoTracks du <video>élément, mais vous ne pouvez pas, le tableau de pistes ne contient qu'un seul élément (la première piste vidéo sur le flux multimédia).

What steps will reproduce the problem? (1) Get two MediaStreams with video tracks (2) Add them to a new MediaStream and attach as srcObject on a videoElement (3) Check the videoElement.videoTracks object and see there is only one track

Demo at https://multiple-tracks-bug.glitch.me/

What is the expected result? I would expect videoElement.videoTracks to have two elements.

What happens instead? It only has the first videoTrack that was added to the MediaStream.

Lire l'article complet.

Cas de repro.

window.onload = () => {
  if('getDisplayMedia' in navigator) warning.style.display = 'none';

  let blobs;
  let blob;
  let rec;
  let stream;
  let webcamStream;
  let desktopStream;

  captureBtn.onclick = async () => {

       
    desktopStream = await navigator.getDisplayMedia({video:true});
    webcamStream = await navigator.mediaDevices.getUserMedia({video: { height: 1080, width: 1920 }, audio: true});
    
    // Always 
    let tracks = [...desktopStream.getTracks(), ... webcamStream.getTracks()]
    console.log('Tracks to add to stream', tracks);
    stream = new MediaStream(tracks);
    
    console.log('Tracks on stream', stream.getTracks());
    
    videoElement.srcObject = stream;
    
    console.log('Tracks on video element that has stream', videoElement.videoTracks)
    
    // I would expect the length to be 2 and not 1
  };

};

About Me: Paul Kinlan

I lead the Chrome Developer Relations team at Google.

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Our team tries to make it easier for developers to build on the web by supporting every Chrome release, creating great content to support developers on web.dev, contributing to MDN, helping to improve browser compatibility, and some of the best developer tools like Lighthouse, Workbox, Squoosh to name just a few.