HarmonyOS 沙箱中的视频怎么获取时长和缩略图

async  uriGetAssets(uri:string) { 
 try { 
  let phAccessHelper = photoAccessHelper.getPhotoAccessHelper(this.context); 
  let predicates: dataSharePredicates.DataSharePredicates = new dataSharePredicates.DataSharePredicates(); 
  // 配置查询条件，使用PhotoViewPicker选择图片返回的uri进行查询 
  predicates.equalTo('uri', uri); 
  let fetchOption: photoAccessHelper.FetchOptions = { 
   fetchColumns: ['duration'], 
   predicates: predicates 
  }; 
  let fetchResult: photoAccessHelper.FetchResult<photoAccessHelper.PhotoAsset> = await phAccessHelper.getAssets(fetchOption); 
  // 得到uri对应的PhotoAsset对象，读取文件的部分信息 
  const asset: photoAccessHelper.PhotoAsset = await fetchResult.getFirstObject(); 
  console.info('asset displayName: ', asset.displayName); 
  console.info('asset uri: ', asset.uri); 
  console.info('asset photoType: ', asset.photoType); 
  // 获取时长 
  let duration: photoAccessHelper.PhotoKeys = photoAccessHelper.PhotoKeys.DURATION; 
  let photoAssetDuration: photoAccessHelper.MemberType = asset.get(duration.toString()); 
  console.info('asset duration: ', photoAssetDuration); 
  // 获取缩略图 
  asset.getThumbnail((err, pixelMap) => { 
   if (err == undefined) { 
    console.info('getThumbnail successful ' + JSON.stringify(pixelMap)); 
   } else { 
    console.error('getThumbnail fail', err); 
   } 
  }); 
 } catch (error){ 
  console.error('uriGetAssets failed with err: ' + JSON.stringify(error)); 
 } 
}