HarmonyOS 鸿蒙Next 如何获取网络视频的第一帧图片？

先下载一段数据到应用沙箱，再通过沙箱资源获取视频缩略图。下载网络视频可参考：
https://developer.huawei.com/consumer/cn/doc/harmonyos-guides-V5/app-file-upload-download-V5#下载网络资源文件至应用文件目录
获取视频缩略图参考：
https://developer.huawei.com/consumer/cn/doc/harmonyos-guides-V5/avimagegenerator-V5

• 接收到的前三帧数据，也可以通过业务需要调整。

• let size: image.Size = {
  width: 640,
  height: 480
  }
  let receiver: image.ImageReceiver = image.createImageReceiver(size, image.ImageFormat.JPEG, 8);
  receiver.on('imageArrival', () => {
  console.info("imageArrival callback");
  receiver.readNextImage((err: BusinessError, nextImage: image.Image) => {
  if (err || nextImage === undefined) {
  console.error("receiveImage -error:" + err + " nextImage:" + nextImage);
  return;
  }
  nextImage.getComponent(image.ComponentType.JPEG, (err: BusinessError, imgComponent: image.Component) => {
  if (err || imgComponent === undefined) {
  console.error("receiveImage--getComponent -error:" + err + " imgComponent:" + imgComponent);
  return;
  }
  if (imgComponent.byteBuffer as ArrayBuffer) {
  let sourceOptions: image.SourceOptions = {
  sourceDensity: 120,
  sourcePixelFormat: 8,
  sourceSize: {
  height: 1080,
  width: 1920
  },
  }
  let imageResource = image.createImageSource(imgComponent.byteBuffer, sourceOptions);
  let imagePackerApi = image.createImagePacker();
  let packOpts: image.PackingOption = { format: "image/jpeg", quality: 90 };
  const filePath: string = getContext().cacheDir + "/image.jpg";
  let file = fs.openSync(filePath, fs.OpenMode.CREATE | fs.OpenMode.READ_WRITE);
  imagePackerApi.packToFile(imageResource, file.fd, packOpts).then(() => {
  console.error('pack success: ' + filePath);
  }).catch((error: BusinessError) => {
  console.error('Failed to pack the image. And the error is: ' + error);
  })
  imageResource.createPixelMap({}).then((res) => {
  this.imgUrl = res;
  });
  } else {
  return;
  }
  nextImage.release();
  });
  });
  });