If anyone bothered to click the link, it's not MIDI but MIDI-generated audio (title should be changed). They used MIDI audio because likely it simplified the problem along a number of dimensions: rhythm and timbre are fixed, and there is no noise. It also means it's cheating and it will not work on acoustic performances, but it's a good start. I mean if you can't solve the problem for MIDI audio you will never solve it for anything else.