A number of moons back, compilers were the topic of the inclusion debate. Considering they can be an integral part of an OS' codebase and it's functioning, it is still in terms of computer science it's very own subject. For something that's highly correlated and lacks an appropriate place elsewhere, it ended being tolerated within the scope.
MP3 is not like a compiler as it is not and will not be an integral design choice in any sane OS design - the same structure would be relevant to formats like OGG or AAC. Secondly, there is already a website referenced with similar functionality where it is an order of magnitude more topical, and would be better there.
@onlyonemac: I don't recall having specific troubles locating documentation on the MIDI (and mod/s3m/xm) format when I tried building my own player for the fun of it - a decade ago. Let it be some sort of consolation that everybody able to use google images
will still find a good run down on MIDI on the page behind the first hit today.
 The interleaving MIDI discussion and everything flowing from it was moved to a separate thread