title: AVPlayer and addPeriodicTimeObserverForInterval does not work when app goes to background
body: <p>Question 1.
  I am seeing following behavior on iphone 4 and iOS 5.0.1 </p>
  
  <ul>
  <li><p>register using addPeriodicTimeObserverForInterval to receive updates every 250 ms and update UI.</p></li>
  <li><p>works well till the app goes to background. For eg. hit the home button or lock the screen,</p></li>
  <li>When app comes back to foreground the player starts playback again but the updates dont fire again. If user hits the play pause button again on the UI updates start firing again.
  This can be seen in the <a href="https://developer.apple.com/library/ios/#samplecode/AVPlayerDemo/Introduction/Intro.html#//apple_ref/doc/uid/DTS40010101" rel="nofollow">demo</a> app from apple as well. </li>
  </ul>
  
  <p>Question 2</p>
  
  <p>Can we not mix C based Audio Session APIs with AV foundation classes? For eg. I have my C based listener registered when AudioInterruptions. But when I use AVPlayer with kAudioSessionCategory_PlayAndRecord they dont get called. When app goes to background AVPlayer pauses without the C based listener getting called.</p>
  
  <p>Is this expected or can I do something? Please note that once I have disposed the AVPlayer instance and my app goes to background again wiht kAudioSessionCategory_PlayAndRecord
   set as category the listener function gets invoked.</p>