title: How to know if an audio unit of type AudioFilePlayer is playing (rendering)
body: <p>I use an AUGraph and it contains some audio units of subtype <code>kAudioUnitSubType_AudioFilePlayer</code>.</p>
  
  <p>I know we can ask if the AUGraph is running thanks to <code>AUGraphIsRunning</code> but I would like to know if an AudioFilePlayer audio unit is currently playing the AudioFileID i.e "produce" sound. I don't see any function like this.</p>
  
  <p>Indeed the graph could "running" but the AudioFilePlayer audio unit could not produce sound (because of: end of audio file, pause, and so on...)</p>