HarmonyOS 通过photoViewPicker.select选择一个mp4视频之后，如何获取对应的缩略图？

import { common } from '@kit.AbilityKit';  
import { fileUri, picker } from '@kit.CoreFileKit';  
import fs from '@ohos.file.fs';  
import { photoAccessHelper } from '@kit.MediaLibraryKit';  
import { dataSharePredicates } from '@kit.ArkData';  
import { image } from '@kit.ImageKit';  
let uri:string = '';  
@Entry  
@Component  
struct PhotoPage {  
  @State imagePath: string = ''  
  @State pixelMap:image.PixelMap  | undefined = undefined  
  private controller:VideoController | undefined  
  private context = getContext(this) as common.UIAbilityContext;  
  
  build() {  
    Row() {  
      Column() {  
        Video({  
          src:this.imagePath,  
          controller: this.controller  
        }).height(300).width('100%').margin({ bottom: 20 })  
        Button("选择视频")  
          .onClick(() => {  
            this.selectPhoto()  
          })  
        Image(this.pixelMap).width(300).height(400)  
      }.width('100%')  
    }.height('100%')  
  }  
  selectPhoto() {  
    const photoSelectOptions = new picker.PhotoSelectOptions();  
    const photoViewPicker = new picker.PhotoViewPicker();  
    photoSelectOptions.MIMEType = picker.PhotoViewMIMETypes.VIDEO_TYPE; // 过滤选择媒体文件类型为IMAGE  
    photoSelectOptions.maxSelectNumber = 1; // 选择媒体文件的最大数目  
    photoViewPicker.select(photoSelectOptions).then((photoSelectResult: picker.PhotoSelectResult) => {  
      const fileUri = photoSelectResult.photoUris[0]  
      uri = fileUri  
      this.getFileInfo(fileUri)  
      this.uriGetAssets()  
    })  
  }  
  async getFileInfo(filePathString: string) {  
    let resFile = fs.openSync(filePathString, fs.OpenMode.READ_ONLY)  
    const dateStr = (new Date().getTime()).toString()  
    // 临时文件目录  
    let newPath = this.context.filesDir + `/${dateStr + resFile.name}`;  
    // 转化路径  
    fs.copyFileSync(resFile.fd, newPath);  
    // 新的路径  
    let realUri = 'file://' + newPath;  
    this.imagePath = realUri  
    console.log(this.imagePath)  
  }  
  
  async  uriGetAssets() {  
    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: [],  
        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);  
      console.info('asset width: ', asset.get(photoAccessHelper.PhotoKeys.WIDTH));  
      console.info('asset height: ', asset.get(photoAccessHelper.PhotoKeys.HEIGHT));  
      console.info('asset title: ' + asset.get(photoAccessHelper.PhotoKeys.TITLE));  
      // 获取缩略图  
      asset.getThumbnail((err, pixelMap) => {  
        if (err == undefined) {  
          this.pixelMap = pixelMap  
          console.info('getThumbnail successful ' + JSON.stringify(pixelMap));  
        } else {  
          console.error('getThumbnail fail', err);  
        }  
      });  
    } catch (error){  
      console.error('uriGetAssets failed with err: ' + JSON.stringify(error));  
    }  
  }  
}