DivX started life as hacked DLL for one of Microsoft's early MPEG-4 part 2 implementations. By default Microsoft only allowed its MPEG-4 codecs to be written to

DivX started life as hacked DLL for one of Microsoft's early MPEG-4 part 2 implementations. By default Microsoft only allowed its MPEG-4 codecs to be written to WMV/ASF containers. The hacked DLL let a DirectShow filter put the MPEG-4 bitstream in an AVI container. Later versions of the DivX codec were full implementations of the ISO MPEG-4 part 2 codec written from scratch. The nominal "DivX" file was an AVI with the DivX video codec and an MP3 audio track. Unfortunately because the codec and format were all sort of hacked together there were lots of different combinations of various DivX, MS-MPEG-4, Windows Audio, and MP3 combinations floating around. In addition people would encode movies with all kinds of different settings trying to eek out a few extra minutes of video on a 700MB CD-R. DivX tried to advertise itself as "the MP3 of video". It was really the clusterfuck of video that only worked because everyone just installed codec packs (K-lite or ffdshow) and hoped for the best.