codec for MP4?

Still running 2008.1. Downloaded a couple of YouTube videos as mp4s,
but mplayer[fails], Amarok[fails], XMMS[fails], vlc[no sound with
version 0.9.3], Kaffeine[no sound], Totem["needs codec" - plays video,
no sound]are having trouble playing them. I thought Fluendo codecs
came with the 2008.1 powerpack, but it would appear not. The plf codec
[faad] doesn't seem to work either. What do I need to do to let me see
both A and V with mp4s, in MD 2008.1?

Thanks,

 rikona

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