Follow the instructions in the link above, they’re excellent.

If you get a few compile errors related to missing files, add these RPMs (excerpt from /var/log/yum.log):

faad2-devel-2.7-1.el5.rf.i386
x264-devel-0.0.0-0.4.20101111.el5.rf.i386
lame-devel-3.99.5-1.el5.rf.i386
a52dec-devel-0.7.4-8.el5.rf.i386
dirac-devel-1.0.2-1.el5.rf.i386
faac-devel-1.26-1.el5.rf.i386
alsa-lib-devel-1.0.17-1.el5.i386
SDL-devel-1.2.10-9.el5.i386
gsm-devel-1.0.13-1.el5.rf.i386
opencore-amr-devel-0.1.2-1.el5.rf.i386
imlib2-1.4.4-1.el5.rf.i386
imlib2-devel-1.4.4-1.el5.rf.i386
ffmpeg-devel-0.6.5-1.el5.rf.i386
libXpm-devel-3.5.5-3.i386
gd-devel-2.0.33-9.4.el5_4.2.i386

I recommend using the package manager, it will save you a lot of time.

If you get an error referencing PIX_FMT_RGBA32, follow the instructions at: http://blog.hostonnet.com/ffmpeg-php-error-pix_fmt_rgba32