Check out the Tempo Planner API.
Song Tempo Detection
This program analyzes an audio file and attempts to determine the tempo (in beats per minute) of that song. Determining the tempo is not a straightforward process and requires a sophisticated algorithm to accurately detect. For this program to be accurate the audio file should be a musical song with a consistent tempo. The program will accept a number of file types but works best with mp3 files. Allowed file types: mp3 (.mp3) wav (.wav) aiff (.aif) Being able to programmatically determine the tempo of a song will allow you to categorize audio files by tempo.
Connect to API