有没有一种方法可以将视频数据从视频标签/ MediaStream发送到OffscreenCanvas？ [英] Is there a way to send video data from a video tag/MediaStream to an OffscreenCanvas?

问题描述

基本上我希望能够有效地执行相同的代码：

Basically I want to be able to perform effectively this same code:

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);
}

仅使用屏幕外画布。我可以通过屏幕上的消息将图像发送给工作人员，但不能发送视频，因为它直接绑定到 HTMLElement 。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 ？

only using an offscreen canvas. I can send images over messages to the worker the offscreen canvas is on, but not video as it's directly tied to an HTMLElement. Is there currently a way to somehow still render video data or a MediaStream in an offscreen canvas?

推荐答案

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：

You can send frames of a video to an OffscreenCanvas in a Web Worker by modifying your script with the following changes:

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

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
  }
});

参考文献

• HTMLMediaElement.prototype.captureStream（）


• MediaStream.prototype.getVideoTracks（）


• new ImageCapture（）


• ImageCapture。 prototype.grabFrame（）



References

• HTMLMediaElement.prototype.captureStream()
• MediaStream.prototype.getVideoTracks()
• new ImageCapture()
• ImageCapture.prototype.grabFrame()

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