ffmpeg question - where do codecs go?

[Vaughn Treude]

Hello all:
I was asking about installing ffmpeg on Mandrake 10 a while back. KevinO 
gave me some advice that helped me to set up rpmdrake corectly so I 
could retrieve stuff automagically off the Internet.  So I got ffmpeg 
installed, and also faac and faad for the standard audio codecs.   These 
installs appeared to succeed.  Yet when I tried to run ffmpeg, it 
couldn't find the aac codec.  I assume it's probably a configuration 
problem.  So I have two questions:
     - Where does ffmpeg expect to find audio codecs?
     - Are codecs libraries or are the some other kind of format?
The files libfaac.so and libfaad.so are in /usr/lib but ffmpeg either 
doesn't know where they are, or I'm mistaken about these being what 
ffmpeg needs.
Thanks!
Vaughn

PS
I know this may not be the most appropriate forum, if anybody knows of 
one, please let me know.  I tried audiocoding.com earlier, but it seems 
to have disappeared.  There's also doom9, on which I just registered, 
but they won't let me post for 5 days!