1. Download the latest atrpms-repo rpm from

http://dl.atrpms.net/el6-x86_64/atrpms/stable/

2. Install atrpms-repo rpm:

# rpm -Uvh atrpms-repo*rpm

3. Install gstreamer-ffmpeg rpm package:

# yum install gstreamer-ffmpeg

[fusion]
name=fusion
baseurl=http://apt.sw.be/redhat/el6/en/x86_64/rpmforge/
enabled=1
gpgcheck=0

[atrpms]
name=atrpms
baseurl=http://dl.atrpms.net/el6-x86_64/atrpms/stable/
enabled=1
gpgcheck=0