Here is how to install ffmpeg:

1 – Create a file named “dag.repo” (no quotes) in “/etc/yum.repos.d”
2 – Copy and paste these lines in it:

[dag]
name=Dag RPM Repository for Red Hat Enterprise Linux
baseurl=http://apt.sw.be/redhat/el$releasever/en/$basearch/dag
gpgcheck=0
enabled=1

You will need a newline at the end of the file.

3 – Then run “yum install ffmpeg ffmpeg-devel” (no quotes)

This should install it with no issues, note that I set gpgcheck=0, if you search for it you will see a lot of people are suggesting: gpgcheck=1 which yields to something like:
warning: rpmts_HdrFromFdno: V3 DSA signature: NOKEY, key ID X