how can i process the ipod library audio file raw data while it playing

After i get the audio file's URL in ipod library with the MPMediaPickerController. Now the question is 开发者_高级运维i want process the file's raw data before it's played. what shoud i do ??

N.B. In the MPMediaPickerController Reference have a fowllow addtion explain.

The URL has the custom scheme of ipod-library. For example, a URL might look like this: ipod-library://item/item.m4a?id=12345 Usage of the URL outside of the AV Foundation framework is not supported.

You can create an AVURLAsset from the URL and from that an AVAssetReaderOutput; with this you can get CMSampleBuffers which have the "raw data" that you want.