The most easy way to install ffmpeg in CentOS is with yum.
First of all, edit /etc/yum.repos.d/CentOS-Base.repo and add those lines at bottm of file:
[dag]
name=Dag RPM Repository for Centos
baseurl=http://apt.sw.be/redhat/el$releasever/en/$basearch/dag
enabled=1

Then, run command:
yum install ffmpeg

Or, you can install from svn:

svn checkout svn://svn.mplayerhq.hu/ffmpeg/trunk ffmpeg

cd ffmpeg
./configure --help

add some parameters, like --enable-gpl, --enable-libmp3lame, etc..

make see more && make install

(if svn command not found, type yum install subversion)

Hope this help