iPhone sdk Edit Tempo of the Music File

I need to Edit the Tempo of Music File which I am Playing 开发者_如何学Goin the Background.Actually I have to Put Button For Fast Slow and Medium tempo and get the Tempo effect related to it.I am looking for some sample code or tutorial which can guide Thanks in advance for any help that u can provide me.

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There seem to be several time stretch pitch shift libraries available:

Dirac, Finch, rt_pvc, and SoundTouch

Dirac advertises their iPhone/iOS port. I haven't used any of them.

You could also roll your own DSP code using the basic phase vocoder algorithm.

Here's another DSP tutorial on time pitch shifting.