Is it possible access raw PCM data from the iphone audio output?

I know I can embed an MP3 and use AudioUnit. But if the user is playing music in the background from their itunes library, is it possible to access that audio data?

This is for an app that shows visual effects, which react to the music.

From what I can tell, it isn't possible, but that's just from lack of finding any information at all, rather than actual confirmation that it can't be done.

If it isn't possible to access the audio stream from the ipod, is it possible to access raw audio output from the Media Player inside an app, or is pretty much not permitted to access raw audio data from the itunes library at all?

EDIT: I found this question: iOS - Access output audio from background program, which say I can't access the audio from a background app. But is it possible to get the audio data from the itunes library if I play it inside the app?