HarmonyOS 如何获取沙箱下视频文件的某一帧画面

试试以下代码，test1.mp4 在沙箱中

public static writeVideo(ctx: Context) {
  let mgr = ctx.resourceManager;
  let buf = mgr.getRawFileContentSync('test1.mp4');
  let file = fileIo.openSync(ctx.cacheDir + '/test1.mp4', fileIo.OpenMode.READ_WRITE | fileIo.OpenMode.CREATE);
  fileIo.writeSync(file.fd, buf.buffer);
}

public static async getVideoPicture(path: string): Promise<PixelMap> {
  let avImageG = await media.createAVImageGenerator();
  let file = fileIo.openSync(path, fileIo.OpenMode.READ_WRITE | fileIo.OpenMode.CREATE);
  avImageG.fdSrc = file;
  let pix = avImageG.fetchFrameByTime(0, media.AVImageQueryOptions.AV_IMAGE_QUERY_NEXT_SYNC, {width: 300, height: 300});
  return pix;
}