canvas获取视频封面及个别电脑获取到空图

PS：获取封面前提是浏览器要支持视频编码格式，不支持就不能通过该方式获取
读取视频封面：

        let video = document.createElement("video");
        video.src = videosrc;
        video.currentTime= 10 // 可能出现黑屏，从10帧
        video.muted = true; // 解决个别电脑获取到空图
        video.autoplay = true; // 解决个别电脑获取到空图
        video.preload = true; // 解决个别电脑获取到空图
        video.addEventListener('loadeddata', async () => {
    
    
          video.pause();
          var canvas = document.createElement('canvas')
          canvas.width = video.videoWidth
          canvas.height = video.videoHeight
          canvas.getContext('2d').drawImage(video, 0, 0, canvas.width, canvas.height)
          const cover = canvas.toDataURL('image/png')
           console.log('图片base64是：'，cover)
          video.remove();
    }}

base64转file：

const convertFile = base64 => {
    
    
  let fileArray = base64.split(','),
    fileType = fileArray[0].match(/:(.*?);/)[1],
    bstr = atob(fileArray[1]),
    n = bstr.length,
    u8arr = new Uint8Array(n)
  while (n--) {
    
    
    u8arr[n] = bstr.charCodeAt(n)
  }
  return new File([u8arr], '文件名', {
    
     type: fileType })
}

下载：

const buttonClick = (base64) => {
    
    
  let file = convertFile(base64)
  const node = document.createElement('a')
  node.href = URL.createObjectURL(file)
  node.download = file.name
  node.click()
  URL.revokeObjectURL(node.href)
  document.body.appendChild(node)
  document.body.removeChild(node)
}