Question

基本上我希望能够有效地执行相同的代码：


const video = document.getElementById('video');
const canvas = document.getElementById('canvas');
const context = canvas.getContext('2d');

const draw = () => {
  context.drawImage(video, 0, 0);
  requestAnimationFrame(draw);
}

video.onplay = () => {
  requestAnimationFrame(draw);
}

仅使用屏幕外的画布。我可以通过消息将图像发送给屏幕外画布处于打开状态的工作人员，但不能将视频直接发送到HTMLElement，因此不能发送视频。当前是否可以通过某种方式仍然在屏幕外的画布中渲染视频数据或MediaStream？

Answer 1

您可以通过以下方式修改脚本，将视频帧发送到Web Worker中的OffscreenCanvas：

const worker = new Worker('my-worker.js');
const video = document.getElementById('video');
const stream = video.captureStream();
const [track] = stream.getVideoTracks();
const imageCapture = new ImageCapture(track);
const canvas = document.getElementById('canvas');
const offscreen = canvas.transferControlToOffscreen();

worker.postMessage({ offscreen }, [offscreen]);

const draw = () => {
  imageCapture.grabFrame().then(imageBitmap => {
    worker.postMessage({ imageBitmap }, [imageBitmap]);
  });

  requestAnimationFrame(draw);
};

video.onplay = () => {
  requestAnimationFrame(draw);
};

`my-worker.js`

let canvas;
let context;

addEventListener('message', event => {
  if (event.data.offscreen) {
    canvas = event.data.offscreen;
    context = canvas.getContext('2d');
  } else if (event.data.imageBitmap && context) {
    context.drawImage(event.data.imageBitmap, 0, 0);
    // do something with frame
  }
});

有没有一种方法可以将视频数据从视频标签/ MediaStream发送到OffscreenCanvas？

1 个答案:

`my-worker.js`

参考文献