I'm lazy, so I'll let the readme do the talking...
DownloadME MP3 Library by jsharrad
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To load and initialize:
music = loadlib ("memp3", "init")
--then make sure it actually loaded
if music then music() end
Functions:
Memp3.play("filename.mp3")
Memp3.stop()
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-- ID3 TAGS ARE NOT SUPPORTED YET --
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If your mp3 has a tag, it won't play.
No variable bitrate mp3s yet either.
subdirs are allowed, just use
Memp3.play("subdir/filename.mp3")
All work is done by the PSP's ME processor
and the threads created by memp3.lrx.
Credits to cooleyes and dark_alex at ps2dev
as this code is based on cooleyes decoder
and dark_alex's atrac3 player
Also, thanks Metallica for the awesome version
of Star Wars Imperial March, used to test it

If you have your own luaplayer v0.20 that you want to use this module with, you'll have to patch the bootstrap loader with this
patch (right click and save as...), then copy to the bootstrap directory and execute the following
cat bootstrap.patch | patch -p0
DownloadEnjoy