一、上传到OSS或者服务器
缺点：
1.大文件上传时间过长
2.如果用户只是预览则会浪费服务端存储

二、使用FileReader对象转换File对象为base64

<input type="file" id="videoInput">
<video src="" alt="预览" id="video" controls="controls">
<script>
  const videoInput = document.getElementById('videoInput');
  videoInput.addEventListener('change', e => {
    previewByReader(e.target.files[0])
  })

function fileToBase64(file: File): Promise<{ url: any, filename: string }> {
  const fileReader = new FileReader()
  fileReader.readAsDataURL(file)
  var filename = file.name;
  return new Promise((resolve, reject) => {
    fileReader.addEventListener("loadend", (e: ProgressEvent<FileReader>) => {
      var url: any = e.target!.result;
      resolve({ url, filename })
    }, false);
  })
}
  async function previewByReader (file) {
   const {url} = await fileToBase64(file)
   video.src = url
  }
</script>

三、通过blob协议实现预览

<input type="file" id="videoInput">
  <video src="" alt="预览" id="video" controls="controls" width="400" height="200">
  <script>
    const videoInput = document.getElementById('videoInput');
    videoInput.addEventListener('change', e => {
      previewByURL(e.target.files[0])
    })
    function previewByURL (file) {
      video.src = URL.createObjectURL(file)
    }
  </script>