MP3PlayerPlugin_v0.12 is released by plum. MP3PlayePlugin is a handy homebrew plugin that allows you to hear your own music while playing games.
Controls (translated by me):The swinging action to optimize how to draw a PSP-HUD can be used with other plug-ins
DownloadL + R + Left / Right = select other songs
2. L + R +  = Pause
3. L + R + O = Change the order of play (in order, randomly, etc.)
4. L + R + Triangle = Play the song again.
5. L + R + Up / Down = change in volume.