There is non-obvious dependency in media-tv/xbmc. In order to play video files with multichannel audio other then ac3 or dts (say, 5.1 aac track) over digital link, it is necessary to convert audio to ac3. XBMC does it quietly if ffmpeg supports encoding. Otherwise there is no audio at all. It could be optional, but there should be some dependency on USE=encode in ffmpeg. Tested with media-video/ffmpeg-0.9 and 0.10 (no rebuild of xbmc necessary).
should be all set now in the tree; thanks for the report! Commit message: Require ffmpeg be built with USE=encode to make things "just work" http://sources.gentoo.org/media-tv/xbmc/xbmc-9999.ebuild?r1=1.97&r2=1.98
