Open source MIDI libraries

I would like to know about open source libraries that could be used to perform some simple tasks on MIDI files:

1. reading a file one note - or chord - at a time;
2. extracting a given instrument to re-encode it separately in a new file;
3. allow to produce a "customizable" score -- by that I mean that I should be able to alter the way the sheet music is produced from the midi using the libraries ... I assume this will require an interaction with Lilypond or Musixtex.

I don't really have a preferred language, as long as it is not too painful to make the app cross-platform. Other advice is welcome -- better to learn it now rat开发者_运维知识库her than when I've already written a lot of code. So far, I've been trying to dig in MuseScore's (C++) source code, but it seems that GUI code permeates most files and although spotting relevant files was easy, it is difficult for me to extract just what I need (I'm only aiming for a command line application right now, I'll see about interfaces later).

Any ideas?

Thanks!

Well, I'm just getting started, but this (in Python) seems promising.

If you're still working on the project and language isn't a problem, you might try Python's cross-platform music21 which can parse midi files into Note, Chord, Instrument, etc., objects, lets you manipulate the scores, and then R/T back to MIDI or output to Lilypond, etc. (full disclosure, I'm the author of the toolkit; but I don't know of many others in any language that will take MIDI in and put Lilypond out while giving you a chance to treat the MIDI elements as objects to manipulate in the meantime.).

Sample code to screw up all the instrument sounds in a MIDI file and then play it and make a lilypond.pdf from it:

 import music21
 mf = music21.converter.parse('pathToMidiFile.mid')
 for x in mf.recurse():
     if 'Instrument' in x.classes:
         x.midiProgram = (x.midiProgram * 2) % 128
 mf.show('midi')
 mf.show('lily.pdf')

Hope that helps.