HarmonyOS 录制的视频转base64

可参考：

async abtainBase64(url:string){
  let fd: number = fileIo.openSync(url, 0o0).fd;
  const file = fs.openSync(url, fs.OpenMode.READ_ONLY);
  let videoSize = fs.statSync(file.fd).size;
  let buffer = new ArrayBuffer(videoSize);
  fs.readSync(file.fd, buffer);
  let helper = new util.Base64Helper();
  let buf: Uint8Array = new Uint8Array(buffer);
  let base64 = '视频格式' + helper.encodeToStringSync(buf, util.Type.MIME);
  console.log("视频格式=====================",base64)
  fs.closeSync(file);
}