I have a couple of movie trailer files that use AAC 5.1 audio. This used to be decoded by libfaad, but is now being decoded by FFmpeg instead ever since this changeset:
user: Torsten Jager
date: Thu Feb 21 22:41:17 2013 +0200
ffmpeg_audio_decoder: enable mpeg4 audio
Unfortunately, the FFmpeg decoder is broken somehow, and causes xine to freeze after a few seconds playback. Possibly FFmpeg is being configured incorrectly because xine-ui's OSD claims that the audio is "1 Hz" instead of "48000 Hz".