''3ivx and XviD
It's more than a coincidence that XviD looks like DivX backwards. Both XviD and the current version of DivX were developed from the same Open Source MPEG-4 project. Where DivX went commercial, XviD remains Open Source. It's a standards-based MPEG-4 codec, and its Open Source status means it has been ported to a wide variety of platforms including Windows, MacOS X, Linux, and a number of other Unix flavours. 3ivx is a commercial version of MPEG-4, and also supports quite a few platforms other than Windows and MacOS. Unlike DivX and XviD, it also includes MPEG-4 audio encoding and decoding.
''H.264, MPEG-4 AVC
The H.264 variant of MPEG-4 has been like the Second Coming of MPEG, gaining so much public interest you almost expect it to cure cancer. Although it's a refinement of MPEG-4, H.264 offers an even better calibre of video at lower bit rates, such as broadcast quality SD at less than 1Mbit/sec. For this reason, it is seen as the saviour of the high definition generation. Both Blu-ray and HD-DVD offer H.264 as an encoding option alongside MPEG-2 and Microsoft VC-1, and the AVCHD camcorder format uses it. It is being used for Sky's satellite HD channels, and the BBC HD trial was broadcast using H.264.
We've added WMV onto the end of the list of MPEG-4 codecs, because its history goes back to Microsoft's own MPEG-4 developments. However, it no longer conforms to the MPEG-4 standard, and instead incorporates proprietary Microsoft special sauce, information about which is kept secret. Although WMV isn't MPEG-4, it is an interframe compression based upon it, although its compression abilities have developed to be on a par with H.264. Hence, the inclusion of Microsoft's VC-1 (based on WMV9) as an option for Blu-ray and HD-DVD.
And that concludes our two-week jaunt through the world of digital video codecs. Watch out for a future week when we return to the subject of video encoding, with specific reference to Internet streaming, and in particular Flash Video.