Lame mp3 encoder project - http://www.mp3dev.org/mp3/
TooLame mp2 encoder project - http://www.cryogen.com/mikecheng
Ogg Vorbis -
http://www.xiph.org/ogg/vorbis
Other Ogg Substreams -
http://www.xiph.org/ogg/index.html
Brians OS/2 Ogg Vorbis Page -
http://silk.apana.org.au/vorbis/
Lame 3.87beta for OS/2 (no frills, 700k)
Lame 3.86 for OS/2 with Vorbis etc (1.6mb)
Lame 3.86 for OS/2 (no extras) (540k)
Vorbis Beta 3 Encoding and Playback
Tools (380k)
Vorbis Beta 3 Developement Stuff (260k)
Vorbis Tools 09/09/2000 (900k)
Lame 3.84 for OS/2 (510k)
Lame 3.82 for OS/2 (500k)
Lame 3.80 for OS/2 (400k)
Lame 3.69 for OS/2 (470k)
Toolame 02g for OS/2 (200k)
Lame 3.88 Source
Lame 3.86 Source
Lame 3.84 Source
Lame 3.82 Source
Lame 3.80 Source
Lame 3.69 Source
Toolame 02h Source
Toolame 02g Source
Vorbis Beta 3 Sources (800k)
Vorbis Nightly from 09/09/2000
To compile Lame and Toolame for OS/2, I used EMX 0.9d, Bash, Sed, gnu-make, gnu-grep and a few other tools. For toolame, you also need gcrt0.o, as it doesn't ship with emx. If you are interested in creating your own build environment, let me know and I'll tell you what I'm using at the moment. To compile vorbis, I mostly just prodded configure till it worked, and commented out code that didn't compile (highly technical). If you're looking to compile it on a more standard emx build system, I'd advise using the source on Brians page (http://silk.apana.org.au/vorbis/), though I'll happly zip and email you my build directories if you want them!
Once you've made your mp3s / vorbis's, you'll need someway to play them back. The main contenders (IMHO), are all avaiable from hobbes in http://hobbes.nmsu.edu/pub/os2/apps/mmedia/sound/players.