title: Change speed (tempo) of playing track in realtime in iOS
body: <p>I'm after writing an app that is essentially based on a very simple DJ metaphor. I want to be able to change the tempo of a track in real time by adjusting a slider.</p>
  
  <p>Can this be done in realtime using the AVAudioPlayer class, or can you only set it while preparing the track for playback?</p>