“Earworm (thanks to Jonathan Feinberg for the name) makes it possible to extend or shrink a song to any length you might desire, without changing the tempo. It does this by constructing a network graph of the piece, using The Echo Nest’s analysis data. Each node in the graph is a beat in the song, and an edge exists between two nodes if the two beats, and the several beats that follow them, sound similar (close in timbre and pitch).” The Echo Nest Blog
They use a tune from Phoenix for the samples. Check it out!