Rubber Band is an audio time-stretching and pitch-shifting library and
utility designed for musical applications.
http://www.breakfastquay.com/rubberband/
It includes a library that supports a sample-accurate multithreaded
offline mode and a real-time lock-free streaming mode; a command-line
utility program; and a LADSPA pitch-shifter plugin. Rubber Band is
Free Software under the GNU GPL.
Chris