如何使用javascript为html格式的视频文件生成缩略图url？

<video id="myVideo" src="video.mp4"></video>

var video = document.getElementById('myVideo');
video.addEventListener('loadeddata', function() {
  // 视频加载完成后执行生成缩略图的操作
});

var canvas = document.createElement('canvas');
var context = canvas.getContext('2d');
canvas.width = video.videoWidth;
canvas.height = video.videoHeight;
context.drawImage(video, 0, 0, canvas.width, canvas.height);
var thumbnailUrl = canvas.toDataURL();

var thumbnailImage = document.createElement('img');
thumbnailImage.src = thumbnailUrl;
document.body.appendChild(thumbnailImage);