Hi,

Well, midi and mp3 aren't really the same kind of thing.

Midi is intended as a standard for recording how music is played on a digital instrument, rather than what the performance sounds like. They can be played back by midi instruments, and quite a few computers have midi players installed to play midi files back as well, implementing a virtual instrument. Providing midi files you have no control over the sound, and especially with generated midi files that include the bare minimum of information to play a note, played midi files will sound like manure. TTBOMK, using the midi standard is free in itself, but it will of course be primarily available on performance-related hardware, not on hardware geared towards play-back only.

MP3 is a standard for compressing files. It's intended for use with audio files, as it's developed by the Moving Picture Experts Group (MPEG) for inclusion of sound in their film files. The compression is done, in part, by leaving out minute details of the sound. This is why, according to a lot of people, an mp3 doesn't sound as good as a CD. TTBOMK, mp3 is patented, which is why open source computers generally don't include mp3 players out of the box. Mp3 players, apart from being a device in themselves, will often be included in hardware geared towards play-back; you're less likely to find it on digital musical instruments.

Converting from midi files to mp3-compressed sound files, again the converter will have to introduce a virtual instrument that will play the midi and whose sound can then be compressed. Obviously, if the midi files include just the bare minimum for the notes to be played, the virtual instrument, just like that of the computer midi player, will sound devoid of any style, as that information isn't present in the generated midi file to begin with. Compressing that sound is not going to add any quality, so it'll still sound like manure.

As you can see from the above, offering midi files and/or mp3 files, is largely a matter of audience(s). But since the mp3 files include the sound, if compressed, for simple midi files the mp3 files will be much larger.

If you do want to convert midi files to mp3 audio files, apart from the options already mention, there are also on-line conversion services. A search like this will lead you to several of those.

Bye
                                                                Mysha