I read the link and this is a rewriting of my last message.
I have 2 movies coded with AAC 5.1 that are played fine using mplayer by itself. That is: both are downmixed correctly to analog stereo, so you can hear dialogs clearly. However, when playing those movies inside XBMC, just ambiance sound are reproduced, and dialog are either at a VERY low volume (almost inaudible), or just not able to hear them at all.
This behavior is reproduced every time I tested it.
First movie (1080)
Second movie (1440)
After a simple check of the logs, my UNeducated guess is that XBMC is failing in open libfaad (from xbmc.log):
>DEBUG: FactoryCodec - Audio: passthrough - Failed
>DEBUG: FactoryCodec - Audio: libfaad - Opening
>DEBUG: Loading: libfaad.so.0
>ERROR: Unable to load libfaad.so.0, reason: libfaad.so.0: cannot open shared object file: No such file or directory
>DEBUG: Dll libfaad.so.0 was not found in path
>DEBUG: FactoryCodec - Audio: libfaad - Failed
While mplayer by other hand seems to have no problem to open it (from mplayer log):
>==========================================================================
>Opening audio decoder: [faad] AAC (MPEG2/4 Advanced Audio Coding)
>AUDIO: 48000 Hz, 2 ch, s16le, 128.0 kbit/8.33% (ratio: 16000->192000)
>Selected audio codec: [faad] afm: faad (FAAD AAC (MPEG-2/MPEG-4 Audio))
>==========================================================================
>AO: [pulse] 48000Hz 2ch s16le (2 bytes per sample)
Additional information:
Hardware
Dell Dimension E520
Pentium D (2 cores), 4Gb RAM.
Geforce 9500 GT 1Gb internal RAM
OS and drivers
Ubuntu Desktop Edition 10.04 (i386)
last update: 8/20/2010
$ uname -a
Linux vaughan 2.6.32-24-generic-pae #41-Ubuntu SMP Thu Aug 19 02:43:57 UTC 2010 i686 GNU/Linux
Nvidia driver 195.36.24
XBMC
$ dpkg -l xbmc
ii xbmc 1:9.11-lucid3 XBMC Media Center (full metapackage)
XBMC 9.11 R26018 (compiled: Aug 19 2010)
Installed from ppa:team-xbmc, following instructions from xbmc wiki.
Skin: Confluence (no other skin installed).