This week I took the MIDI Player that I utilized in my HoloValentine App. The source code originally came from a project in CodePlex. The license was a MIT license and the code was originally created for XNA.
I took that and code from folks who had done similar work in Unity and cleaned up some bits to create a MIDIPlayer project that should easily load into any Unity project.
This video is where I show checking in the latest change of creating a demo scene that plays a MIDI file on demand. The MIDI file loops, but the MIDIPlayer script can be updated to allow for a playlist.
If you are looking to play MIDI files in your Unity project, I hope this helps you!
http://chd.me/CSharpSynthForUnity
http://chd.me/holovalentine [source code for HoloValentine App that uses the player]