Hello,
I was wondering if FLAC works with Solarus. Obviously, it isn't a big deal because ogg works, but I was just wondering. :D
According to the documentation no, the only format allowed are .ogg, .it and .spc, checked in this order. See http://www.solarus-games.org/doc/latest/lua_api_audio.html#lua_api_audio_play_music for more details.
Poor FLAC....it never really gets supported. The open source forever alone audio format.