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.videoWidthcanvas.height = video.videoHeightcanvas.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.namenode.click()URL.revokeObjectURL(node.href)document.body.appendChild(node)document.body.removeChild(node)
}