我们如何使用mediaRecorder将画布流与音频流混合

Question

我有一个使用canvas.captureStream()的画布流.我有来自webrtc视频通话的另一个视频流.现在我想将画布流与视频流的音轨混合在一起.我怎么能这样做？

Answer 1

使用Firefox 和 Chrome 56 中可用的MediaStream构造函数将曲目组合到新流中：

let stream = new MediaStream([videoTrack, audioTrack]);

以下内容在 Firefox 中适用于我（在 Chrome 中使用https fiddle，尽管它在录制时出错）：

let stream = new MediaStream([videoTrack, audioTrack]);

navigator.mediaDevices.getUserMedia({audio: true})
  .then(stream => record(new MediaStream([stream.getTracks()[0],
                                          whiteNoise().getTracks()[0]]), 5000)
    .then(recording => {
      stop(stream);
      video.src = link.href = URL.createObjectURL(new Blob(recording));
      link.download = "recording.webm";
      link.innerHTML = "Download recording";
      log("Playing "+ recording[0].type +" recording:");
    })
    .catch(log))
  .catch(log);

var whiteNoise = () => {
  let ctx = canvas.getContext('2d');
  ctx.fillRect(0, 0, canvas.width, canvas.height);
  let p = ctx.getImageData(0, 0, canvas.width, canvas.height);
  requestAnimationFrame(function draw(){
    for (var i = 0; i < p.data.length; i++) {
      p.data[i++] = p.data[i++] = p.data[i++] = Math.random() * 255;
    }
    ctx.putImageData(p, 0, 0);
    requestAnimationFrame(draw);
  });
  return canvas.captureStream(60);
}

var record = (stream, ms) => {
  var rec = new MediaRecorder(stream), data = [];
  rec.ondataavailable = e => data.push(e.data);
  rec.start();
  log(rec.state + " for "+ (ms / 1000) +" seconds...");
  var stopped = new Promise((y, n) =>
      (rec.onstop = y, rec.onerror = e => n(e.error || e.name)));
  return Promise.all([stopped, wait(ms).then(_ => rec.stop())]).then(_ => data);
};

var stop = stream => stream.getTracks().forEach(track => track.stop());
var wait = ms => new Promise(resolve => setTimeout(resolve, ms));
var log = msg => div.innerHTML += "<br>" + msg;