Audio Processing library for changing Tempo, Pitch and Playback Rates

SoundTouch is a LGPL-licensed open-source audio processing library for
changing the Tempo, Pitch and Playback Rates of audio streams or
files. The SoundTouch library is suited for application developers
writing sound processing tools that require tempo/pitch control
functionality, or just for playing around with the sound effects.

The SoundTouch library source kit includes an example utility
SoundStretch which allows processing .wav audio files from a
command-line interface.