Can't play AAC (mp4) files, the ffmpeg plugin is present

MOC has an ffmpeg plugin and supports all audio files that can be played by ffmpeg. The problem is that ffmpeg can be build without AAC support. This affects current Debian (as time of writing) which has the ffmpeg package without AAC support (--enable-faad2). The solution is to compile the library yourself.

Mplayer distributed with Debian uses it's own version of the ffmpeg library so it can play AAC.