CentOS is not a great distro for normal HOME use
as you are finding out
Things like multimedia are a "pain in the rear end "
-- as in a dry corn cob in there --
the repo that music and video programs are in, is "rpmforge" and in a few others .
and rpmforge can be incompatible with OTHER repos
to ad into the problem there is NO REAL documentation on HOW to install multimedia
CentOS is a rebuild of RedHat and USES THE SERVER DOCUMENTATION FROM REDHAT
You can PORT the instructions from Fedora ( VERY WELL DOCUMENTED !!!!) for use in CentOS
-- a VERY good Fedora guide is mjmwired
You have to port those instructions and some names ARE DIFFERENT
also see the CentOS wiki, but most of that is fedora 5 and some 6 , no real 7 information
mainly because CentOS is a clone of RHEL and uses the redhat documentation