AV and MediaPlayer Foundations

[thanatos0801]

I'm trying to work with some of the new AV Foundation classes added in
iOS 4. Specifically, I'm looking at the AVPlayer class. It has a
rate property, but the documentation for it is really quite lacking.
What is says is:

0.0 means “stopped”, 1.0 means “play at the natural rate of the
current item”.

However, I've been playing with it. First, it appears that the
granularity is in 0.1 increments instead of being continuous. Second,
it DOES appear to support values > 1.0, but values of 1.1 and above
APPEAR to switch directly to playback at 2X speed.

Does anybody have experience with using the rate property of the
AVPlayer class or have contacts in Apple that might be able to shed
some light on its behavior? What I'd REALLY like to do is have a
UISlider that can change the playback speed of a song in the iPod
library between 0.5 and 1.5X standard playback speed contiguously. I
have DSP code that can do that, but only on files, and from what I can
see Apple doesn't allow access to the actual FILES in the audio
library in any way at all, so if I were to use the DSP code, I'd had to load up another copy of the music into my app separately from the iPod library.

Thoughts?