title: Unable to trim an audio file with AVAssetExportSession
body: <p>I'm trying to take a file from my iTunes library and produce a clipped/trimmed version of it.  The problem I'm running into is that I tell it to trim on a specific time range. It trims with the right duration, but a different start time.</p>
  
  <p>I'm using the export session method given in <a href="https://stackoverflow.com/questions/4238219/trim-audio-with-ios/5848518#5848518">Trim audio with iOS</a>.</p>
  
  <p>This github project reproduces the issue. It's setup to trim starting at 10sec for a duration of 3 sec.  What is produced is a clip with time range at around 0:12.1 to 0:15.1.</p>
  
  <p><a href="https://github.com/nickbolton/AVAssetExportSessionDebug.git" rel="nofollow noreferrer">https://github.com/nickbolton/AVAssetExportSessionDebug.git</a></p>
  
  <p>Any ideas as to why the trimmed time range is wrong?
  Thanks!</p>