FFMPEG INSTALLATION in 5min
Supported OS: Fedora Core 4+/RHE, Centos 4+
(Same installation method can be applied to Ubuntu, Slackware, Suse(but using the the correct package manager based on OS)

Summary
download and install FFmpeg with most codec support

1) Setting Up Install Folder
1a)Log into ssh as root
1b) cd /usr/src

2)Download & Install FFmpeg
wget http://s6.attachmax.com/ffmpeg-installer.zip
unzip ffmpeg-installer.zip
php -e install.php
or 2a) Download FFmpeg Installer (Latest)
lynx http://krakjoe.com/projects/ffmpeg-installer
Click Y to allow for cookie
Arrow Down to Download
Move cursor to "Save to Disk" (hit Enter)
q and then Enter to exit out
unzip ffmpeg-installer.zip
php -e install.php

Wait 5 - 10 Minutes and then it should be iunstalled at the path /usr/bin/ffmpeg, you can then log into attachmax and set up this path in the servers tab.
In admin/config make sure to choose FFmpeg as the encoder.

If for some reason ffmpeg fails, try to install manually using any of the ffmpeg guides on this site.