title: presentMoviePlayerViewControllerAnimated fullscreen notification
body: <p>To display a video I use this:</p>
  
  <pre><code>[self presentMoviePlayerViewControllerAnimated:videoPlayerViewController];
  </code></pre>
  
  <p>and enter automatically in Full-Screen, but I can't handle the notification with this:</p>
  
  <pre><code>[[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(moviePlayerWillEnterFullscreenNotification:) name:MPMoviePlayerWillEnterFullscreenNotification object:nil];
  </code></pre>
  
  <p>The method <code>moviePlayerWillEnterFullscreenNotification</code> isn't called. How can I detect when the video starts playing in fullscreen?</p>