SoundTouch is an open-source audio processing library for changing the Tempo, Pitch and Playback Rates of audio streams or audio files
Tempo (time stretch): Changes the sound to play at faster or slower tempo than originally without affecting the sound pitch.
Pitch (key) : Changes the sound pitch or key while keeping the original tempo (speed).
Playback Rate : Changes both tempo and pitch together as if a vinyl disc was played at different RPM rate.
The SoundTouch library is intended 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 also an example utility SoundStretch that uses SoundTouch library for processing .wav audio files from command-line interface.