I just updated LightMP3 to play FLAC. I had previously posted in a different thread, but I realized it might be seen as hijacking someone else's dev thread, so I'm making my own.
I had originally made a post on ps2dev on how to compile libFLAC for the PSP. You'll find that here:
Someone in another thread here was asking about playing FLAC, and I remarked that it would be pretty simple to add FLAC to LightMP3. So I went ahead and did so. This is the latest LightMP3 (checked out of the subversion repository) with a flac player driver added to it.
Put your FLAC files anywhere, but ms0:/MUSIC/ is always a good place. To avoid having the XMB player trying to play them, put them a level deeper. I put the album folders in ms0:/MUSIC/flac/.
I call it beta because there's one BIG bug - the playspeed and suspend don't work with FLAC (they're both almost certainly the same issue since they use the same command). So don't try to suspend while playing FLAC files, and don't try to use the playspeed function (left/right). Otherwise, it seems to be doing pretty good for me. It even reads the tags in the files. I'm running it on a PSP Slim with 3.71 M33-3.
This archive includes the binary as well as the source folder. You don't need the source to use it - it's just for devs and people interested in those that sort of thing.