If you need to install FFMPEG, the easiest way to do it is with yum. You can run this command to install it.
root@server[/]#yum install ffmpeg ffmpeg-devel
If you run that command and you get package not found, you just need to add the repository for the dag packages to yum. To do that, you will want to create the file /etc/yum.repos.d/dag.repo
then add this in it
name=Dag RPM Repository for Red Hat Enterprise Linux
Then save the file.
After that, go ahead and add the key for the repository so you don’t receive any key errors.
root@server[/]#rpm -Uhv http://apt.sw.be/redhat/el5/en/i386/rpmforge/RPMS/rpmforge-release-0.3.6-1.el5.rf.i386.rpm
Once you do that, you should be able to install those packages with yum without a problem.