Today, I've installed mplayer (marillat-package) on my Debian Sarge system and mplayer-plugin. Everything went fine exept the missing sound in movie trailers (from http://www.apple.com/trailers/\). I can watch the movies inside mozilla-firefox-1.0.1 but I don't hear anything.
Strange thing - when I watch a localy stored clip sound works perfect (alsa). Even stranger: The quicktime and avi-files on the 'plugger testing grounds' (http://fredrik.hubbe.net/plugger/test.html)play sound with the clips.
Now I'm looking for a helping hand:-)!
From the FAQ
If the trailer plays but there is no sound, this can be caused by mplayer not being compiled with FAAD support. FAAD is the AC3 decoder that is needed to decode the audio in some quicktime files. This can also be caused by missing or unsupported codecs.
Make sure you have the essential codecs for mplayer installed.
... sorry, shame on me - I forgot to install win32-codecs. Now I have made up for it and everything works fine:-)!