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. Version 1.2 is
faster in most situations, better sounding in many, and less
potentially subject to patent claims than version 1.0.1 was.
Rubber Band is Free Software under the GNU GPL.
Chris