关于javascript:通过canvas获取视频第一帧封面图

let video = document.createElement('video');video.style="width:0;height:0;position:fixed;right:-100%;"video.muted = 'muted';video.autoplay = 'autoplay';video.onloadeddata = function() {  let { width, height } = getVideoSize(120, this.videoWidth, this.videoHeight);  let canvas = document.createElement('canvas');  canvas.width = width;  canvas.height = height;  canvas.getContext('2d').drawImage(this, 0, 0, width, height);  // 视频转换为图片  canvas.toDataURL('image/png')  document.body.removeChild(video);}video.src = URL.createObjectURL(file.files[0]); // file本地文件document.body.appendChild(video);// 获取视频等比缩放宽高function getVideoSize(maxWidth, width, height) {  if(maxWidth >= width) {    return {      width,      height    }  } else {    return {      width: maxWidth,      height: Math.floor(maxWidth / width * height)    }  }}