I started making a synthesizer, which would take a single instrument sample, and change its pitch via the undocumented audio api.
After I got that wired up, I found a MIDI.lua file that would take a .mid file and load it into a 'score' or 'opus' table.
Here, I just winged it. I started by looping through all the song's track data , and started to build code to split channels into different instruments, etc. This is definitely not 'by the book' by any means, as I couldn't find a book... (lots of good references in the main.lua though)
I went through many stages and phases where the sound was popping terribly, notes were being missed, tempo was completely off, etc.
Source Code: (try it yourself! I've only tried it in the Mac Simulator, let me know how it works for you)