I seen where a lot of server management companies are charging big bucks for this, so this might save you some time and money.

First

nano -w /etc/yum.repos.d/dag.repo

Insert

[dag]
name=Dag RPM Repository for Red Hat Enterprise Linux
baseurl=http://apt.sw.be/redhat/el$releasever/en/$basearch/dag
gpgcheck=1
enabled=1

Then yum update and search for ffmpeg and install all ffmpeg packages including devel.

Seems there is some lib problems along the way so in /etc/ld.so.conf

add

/usr/local/lib

then

ldconfig -v

To install the php extension follow the simple directions on http://ffmpeg-php.sourceforge.net/

Then you should be all set!