Avidemux

Avidemux is a free video editor. It is not really designed for beginners so if you have no experience with video editors this is probably not the right application to choose.

Avidemux is available for Linux, BSD, Mac OS X and Microsoft Windows and is designed for simple cutting, filtering and encoding tasks. It supports many file types, including AVI, DVD compatible MPEG files and MP4. 

It has one of the only Graphic User Interfaces (GUI) for encoding files that works on different platforms. It's quite advanced in what it can do but is not the most user friendly of applications. However there are some presets available and it is possible to save custom settings that may make it easier for beginner users to operate.