title: iPhone SDK: Is it possible to process audio file from local library
body: <p>Well, I will try best not to make it as a 'I just want the code' question...</p>
  
  <p>I'm recently working on a project which requires some audio signal processing from local music files (e.g. iTunes Library). The whole work includes: </p>
  
  <ol>
  <li>Get the PCM data of an audio file (normally from iTunes library);  &lt;--AudioQueue (?)</li>
  <li>Write the PCM data to a new file (it seems that Apple does not allow direct modification on music tracks);  &lt;--CoreAudio(?)</li>
  <li>Do some processing and modification, like filters, manipulators, etc. &lt;-- Will be developed in C++</li>
  <li>Play the processed track. &lt;--RemoteIO</li>
  </ol>
  
  <p>The problem is, after going through some blogs and discussions:</p>
  
  <p><a href="http://lists.apple.com/archives/coreaudio-api/2009/Aug/msg00100.html" rel="nofollow noreferrer">http://lists.apple.com/archives/coreaudio-api/2009/Aug/msg00100.html</a>, <a href="http://atastypixel.com/blog/using-remoteio-audio-unit/" rel="nofollow noreferrer">http://atastypixel.com/blog/using-remoteio-audio-unit/</a></p>
  
  <p><a href="http://osdir.com/ml/coreaudio-api/2009-08/msg00093.html" rel="nofollow noreferrer">http://osdir.com/ml/coreaudio-api/2009-08/msg00093.html</a></p>
  
  <p>as well as the official sample codes, I got a feeling that the CoreAudio SDK allow us to apply audio processing <strong>only on voice demos recorded from Mic</strong>.</p>
  
  <p>My question is that: </p>
  
  <ol>
  <li>Can I get raw data from <strong>iTunes library tracks</strong> instead of Mic input?</li>
  <li>If the first question is 'No', is there a way to 'fool' the SDK to let it think it is getting data from Mic input, not from iTunes? (I have done some similar 'hacking' stuff in C# before XD)</li>
  <li>If the whole processing just doesn't work, can anyone provide some alternative ideas?</li>
  </ol>
  
  <p>Any help will be appreciated. Thank you very much :-)</p>
  
  <p>Thanks.</p>