title: Getting the AVAssetReader's Sample Data
body: <p>I'm trying to get the PCM data from an MP3. I'm using <code>AVAssetReaderOutput</code> and it seems to reading the data fine.</p>
  
  <pre><code>while(true)
  {
      nextBuffer = [assetReaderOutput copyNextSampleBuffer];
  
      if(nextBuffer)
      {
  
         countsample = CMSampleBufferGetNumSamples(nextBuffer);
         NSLog(@"%i", countsample);
      }
  
  }
  </code></pre>
  
  <p>I noticed that if I add up <code>countsample</code>, it equates to the number of seconds in the song (assuming 44100hz sample rate). For this reason, I'm sure the reading is being handled perfectly. What I'd like to do, however, is perform various DSP filters on this data but I need to do it on the sample information itself. How can I access the sample data? Also, I noticed that the <code>CMSampleBufferGetNumSamples</code> always returned <code>8192</code> except at the end of the song. Is there a way to increase/decrease this read rate?
  Thank you</p>