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!

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

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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.