title: AVAssetExportSession working in background
body: <p>I tried to manage AVAssetExportSession working when app in background. I have iOS 6 device and testing it there. So i m making audio mix and trying to export audio. When app is in foreground i m making all OK, but if i m going to background i m getting AVAssetExportSessionStatusFailed and have to create it from beginning. So, is it ever possible to make audio mixing work in background?</p>
  
  <p>I m trying to make [exportSession exportAsynchronouslyWithCompletionHandler: ] in NSOperationQueue or getting global queue - but the results is the same - it stops when app going in background and sending failed afterwards. </p>
  
  <p>Does anyone have an example with AVAssetExportSession working in background?</p>