while trying to make flowplayer work with audio files I have seen quite a few users having trouble with it. One basic symptom is that the onStart event never is triggered, which results in the audio file never starting to play. Various postings refered to the id3 information/tags inside the audio being required, which didn't make a change for me.

I now discovered that the audio pluggin seems to support "only" MPEG1 Audio Layer 3. Converting all of the audio files into the proper(?) encoding (Layer 3 / "true .mp3"?) it seems to work mostly fine.

Is Layer3 the only audio format supported? Will this change anytime, as it seems that for example Layer2 is widely supported by other applications?

Anyway, if you have trouble with audio files, make sure they are in Layer3 enconding:http://de.wikipedia.org/wiki/MPEG-1_Audio_Layer_3, to convert you can for example use ffmpeg:
ffmpeg -i myinputfile.mp3 myoutputfile.mp3