Calculate Beats-Per-Minute of a Song (Mac OS X)

This project is for a program that can calculate the beats-per-minute (BPM) of an MP3 file. This code will be integrated in to a larger XCode / Cocoa project so it will need to be written as a module or class or script that can be easily integrated in to another project. Instructions on integrating it in to the larger project should be provided. Speed is important - the BPM will need to be calculated in 5 seconds or less (to speed things up, it is OK if the program samples only a portion of the song rather than the whole thing). MP3 files are the most important but I am willing to pay more if the program can also calculate the BPM for other file types such as WMA, AAC, MP4, OGG etc.