"Moonlight" over at the PS2Dev forums has just released simple piece of homebrew that allows users to play sounds and music encoded in the PSP's proprietary ATRAC3 format, presumably from game UMDs. While the author makes it clear that the program is simply a proof of concept, and still fairly buggy, the player still might be worth a look.

"This is a sample showing a simple atrac3 player using the libatrac3plus from the firmware.

This program does not pretend to be a serious player, it's only a sample on how to use the sceATRAC3plus_Library, and it have some bugs or incorrect code, mainly:

- The player supposes that all frames of the file have 1024 or 2048 sound samples, which is true in almost all cases, but not always.
- There is a bug in which sometimes one of the threads cannot be created because the previous copy of the thread is already running (probably, because of a deadlock). "


Download: [AT3Player]

(Thanks for the email, roberto!)