DivX Codec

To play DivX videos, simply download the latest version available for your system and follow the installation instructions:

DivX codec v6.1.0 for Windows XP/2000 (11.4MB)
DivX codec v5.2.1 for Windows ME/98 (7.6MB)
DivX codec v6.0.0 for Mac OS X (4.8MB)
DivX codec v5.1.1 for Mac (2.1MB)

When you install the codec it essentially works as an add-on to your system, which enables you to compress and decompress video in the DivX format. Once you’ve installed the codec on your system you will be able to watch DivX movies using Windows Media Player or any other player that supports DivX.

The DivX codec is currently the most popular MPEG-4 based codec because of its quality, speed and efficiency as well as the wide range of DVD players that support DivX.

Wiki on ‘What are codecs?’