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从视频流获取数据URL?

webm webrtc stream video javascript

Mitya · 技术社区 · 7 年前

我有一个视频(webm)捕获脚本,效果很好。它录制视频,然后提供下载。代码的相关部分如下:

stopBtn.addEventListener('click', function() {
    recorder.ondataavailable = e => {
        ul.style.display = 'block';
        var a = document.createElement('a'),
            li = document.createElement('li');
        a.download = ['video_', (new Date() + '').slice(4, 28), '.'+vid_format].join('');
        a.textContent = a.download;
        a.href = URL.createObjectURL(stream); //<-- deprecated usage?
        li.appendChild(a);
        ul.appendChild(li);
    };
    recorder.stop();
    startBtn.removeAttribute('disabled');
    stopBtn.disabled = true;
}, false);

URL.createObjectURL 已弃用,我应该使用HTMLMediaElement srcObject 相反

a.href = URL.createObjectURL(video.srcObject);

src 和 currentSrc

2 回复 | 直到 7 年前

Kaiido NickSlash 7 年前

我真的很惊讶你的代码居然能工作。。。

stream MediaStream ,那么浏览器甚至不应该知道需要下载的大小,因此不应该知道何时停止下载(这是一个流)。

MediaRecorder#ondataavailable 将以 data

const stream = getCanvasStream(); // we'll use a canvas stream so that it works in stacksnippet
const chunks = []; // this will store our Blobs chunks
const recorder = new MediaRecorder(stream);
recorder.ondataavailable = e => chunks.push(e.data); // a new chunk Blob is given in this event
recorder.onstop = exportVid; // only when the recorder stops, we do export the whole;
setTimeout(() => recorder.stop(), 5000); // will stop in 5s
recorder.start(1000); // all chunks will be 1s

function exportVid() {
  var blob = new Blob(chunks); // here we concatenate all our chunks in a single Blob
  var url = URL.createObjectURL(blob); // we creat a blobURL from this Blob
  var a = document.createElement('a');
  a.href = url;
  a.innerHTML = 'download';
  a.download = 'myfile.webm';
  document.body.appendChild(a);
  stream.getTracks().forEach(t => t.stop()); // never bad to close the stream when not needed anymore
}


function getCanvasStream() {
  const canvas = document.createElement('canvas');
  const ctx = canvas.getContext('2d');
  ctx.fillStyle = 'red';
  // a simple animation to be recorded
  let x = 0;
  const anim = t => {
    x = (x + 2) % 300;
    ctx.clearRect(0, 0, 300, 150);
    ctx.fillRect(x, 0, 10, 10);
    requestAnimationFrame(anim);
  }
  anim();
  document.body.appendChild(canvas);
  return canvas.captureStream(30);
}

URL.createObjectURL(MediaStream) 用于 <video> 元素。但这也给浏览器关闭物理设备访问带来了一些困难,因为BlobURLs的生存期可能比当前文档更长。
createObjectURL 使用MediaStream,并且应该使用 MediaElement.srcObject = MediaStream 相反

Nimantha Thatkookooguy 3 年前

让我们分步骤进行:

video.srcObject=stream

然后,您需要将具有帧的可变视频转换为画布元素,我们可以通过以下方式实现:

var canvas = document.createElement("canvas");
var ctx    = canvas.getContext('2d');

ctx.drawImage(video, 0, 0)

var du = canvas.toDataURL()