By the way, it would really help if WAV files could be played as well... It looks like they're accepted by the application, but they don't play, and the problem with mp3 files is they have a slight delay in the beginning which can affects intricate time dependent syncing thingies like these kinds of programs
ogg would be a better compressed file to use (better quality with same the same bitrate too)
on top of that, i found a bug that makes it impossible to compensate for this... when i add an offset of 0.03 for example the whole thing glitches out in the render basically, and a whole bunch of other glitches that i can't bother to explain right now but i'm sure you know why and how it happens