title: Avplayer showing black screen sometimes but sound is fine
body: <p>I am using AVPlayer with AVPlayerViewController. I am playing video after adding watermark in the video. Sometimes it is working fine, but sometimes it shows only a black screen, and audio is fine in both cases.</p>
  
  <pre><code>vPlayer = [AVPlayer playerWithURL:_videoFilePath];
  // create a player view controller
  AVPlayerViewController *controller = [[AVPlayerViewController alloc]init];
  controller.videoGravity=AVLayerVideoGravityResizeAspect;
  controller.player = vPlayer;
  [vPlayer seekToTime:kCMTimeZero];
  
  // show the view controller
  [self addChildViewController:controller];
  [vPlayer play];
  controller.view.frame =_imgForVidFrame.frame;
  [self.view addSubview:controller.view];
  </code></pre>