The
Windows 7 Codec Pack is a simple to install package of audio and video
codecs / filters / splitters used for playing back music and movie
files. After installation you will be able to play 99.9% of files on
the internet.

Also included in the package are a number of
encoder codec's, allowing you to encode files in formats such as DivX.
XviD, x264 and many more in your favourite encoding application