HarmonyOS鸿蒙Next中video设置加载图闪屏

方案一：给video设置预览图片

方案二：给video设置显隐控制，在video进入start状态时，在start回调里，控制video展示，示例代码如下：

@Entry
@Component
struct HeiSebeijing {
  build() {
    Row() {
      Column() {
        Text('before')
        VideoComponent({url:'https://img.mcd.cn/cms/images/e3fa083cab2a0851.mp4'})
        Text('after')
      }
      .width('100%')
    } 
    .height('100%')
  }
}
@Component
struct VideoComponent {
  @State isVisibile:Visibility=Visibility.Hidden
  controller: VideoController = new VideoController();
  private url:string=''
  build() {
    Row() {
      Video({ src: this.url, controller: this.controller })
        .visibility(this.isVisibile)
        .autoPlay(true)
        .loop(true)
        .controls(false)
        .width('100%')
        .height('200vp')
        .onStart(() => {setTimeout(()=>{ this.isVisibile=Visibility.Visible  },100) })
        .onPrepared(()=>{ this.controller.setCurrentTime(0,SeekMode.NextKeyframe) }) 
    } 
  } 
}