title: AVQueuePlayer/AVPlayer loading notification?
body: <p>I have an <code>AVQueuePlayer</code> (which obviously extends <code>AVPlayer</code>) that loads a playlist of streaming audio. Streaming is all working fine, but I'd like to have an activity indicator to show the user audio is loading. Trouble is, I can't seem to find any such Notification in <code>AVQueuePlayer</code> (or <code>AVPlayer</code>) that would indicate when the audio buffer has finished loading/is ready to play (nor does there appear to be a delegate method). Any thoughts?</p>