Paul Lamere from The Echo Nest made an awesome music analysis demo called "The Infinite Jukebox" (for when your favorite song just isn't long enough), for automatically finding loopable points in music. And it can use that analysis to stretch a song out to any duration you want, by seamlessly skipping and looping parts of it to shorten or stretch it. It's interactive, so you can point and click on the arcs to control how it loops at any point.
For when your favorite song just isn't long enough
This web app lets you upload a favorite MP3 and will then generate a never-ending and ever changing version of the song. Infinite Jukebox uses the Echo Nest analyzer to break the song into beats. It plays the song beat by beat, but at every beat there's a chance that it will jump to a different part of song that happens to sound very similar to the current beat. For beat similarity the uses pitch, timbre, loudness, duration and the position of the beat within a bar. There's a nifty visualization that shows all the possible transitions that can occur at any beat. Built at Music Hack Day Boston 2012.
