time compression (Score 2, Interesting)

Basically what you want to do is some time compression. You can do that by means of granulation or a FFT. Most audio applications already have time compression/expansion plugins built in to them. Sound Forge, Pro Tools Free, Live and Cool Edit are some of the commercial programs that come to mind. You could also build a stand alone program fairly easily with Csound, Max/MSP or Pure Data. These are audio programming/scripting languages. Csound and Pure Data are free. You just need to know a little about digital audio to make a program with any of those languages.