HarmonyOS 后台播放视频问题

按照官方的demo申请长时任务，后台播放视频，但是没有生效。

async startContinuousTask(): Promise<void> {
  let wantAgentInfo: wantAgent.WantAgentInfo = {
    wants: [
      {
        bundleName: "com.samples.mediaprovider",
        abilityName: "com.samples.mediaprovider.EntryAbility"
      }
    ],
    operationType: wantAgent.OperationType.START_ABILITY,
    requestCode: 0,
    wantAgentFlags: [wantAgent.WantAgentFlags.UPDATE_PRESENT_FLAG]
  };
  let want = await wantAgent.getWantAgent(wantAgentInfo);
  await backgroundTaskManager.startBackgroundRunning(GlobalContext.getContext()
  .getObject('context') as (common.UIAbilityContext), backgroundTaskManager.BackgroundMode.AUDIO_PLAYBACK, want);
}