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

Paul Kinlan
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El primer problema que encontré al intentar construir un editor de video en la web.

Tengo varias secuencias de video (computadora de escritorio y cámara web) y quería poder alternar entre las secuencias de video en un elemento de video para poder cambiar rápidamente entre la cámara web y la computadora de escritorio y no interrumpir el MediaRecorder.

Parece que deberías poder hacerlo alternando la propiedad selected en el objetovideoTracks en el <video> Elementopero no puede, la matriz de pistas contiene solo 1 elemento (la primera pista de video en MediaStream).

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.

Leer publicación completa.

Caso 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
  };

};

Paul Kinlan

Trying to make the web and developers better.

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