embedded AVPlayerViewController reads video partially but did not play

I'm using AVPlayerViewController to play back a remote video asset. It works when I use presentViewController: animated: completion: to pop up the controller.

But it stopped working when I embed AVPlayerViewController in a UIView as following:

  [avPlayer play];

  [videoView addSubview:playerController.view];
  playController.view.frame = videoView.bounds;

I also tried to move [avPlayer play] after the view frame setting, did not work either. The view shows a black background with a play button in the middle. (See attached screenshot).

In more details, I use a delegate to handle the video asset reading via AVAssetResourceLoader setDelegate: queue: , the logs of the delegate shows that when embedding the AVPlayerViewController, the player did read the video URL a few times (4 requests) but then stopped for apparent no reason.

By a request, I mean the following callback was called: resourceLoader:shouldWaitForLoadingOfRequestedResource:

In the failed case, the last request tries to read the last part of the video even though it has not read the previous parts yet:

<AVAssetResourceLoadingDataRequest: 0x60000163be40, requested offset = 8842658, requested length = 4156, requests all data to end of resource = YES, current offset = 8842658>>

In contrast, when using presentViewController to play back successfully, the last request was reading a much larger length of the video till the end.

<AVAssetResourceLoadingDataRequest: 0x6000005b4620, requested offset = 15884, requested length = 8765940, requests all data to end of resource = NO, current offset = 15884>>

Is there any known issue with embedding AVPlayerViewController in a UIView? especially when using custom delegate to handle URL asset read?

Thanks!