Assuming you have Livna or another third party repo:
http://rpm.livna.org/rlowiki/UsingLivna
Try searching for everything gstreamer:
yum search *gstreamer*
then pick out ALL the plugins, once installed they should get picked up, if not just run the following in a terminal as a regular user not root:
rm -rf .gstreamer-0.10
gst-inspect-0.10
That should show you everything gstreamer is setup to handle.