ID3 tag equivalent for video?

[Nicholas Leippe]

http://en.wikipedia.org/wiki/Comparison_of_container_formats

divx created the mpeg-4 codec

xvid is merely an encoder, producing MPEG-4 ASP encoded video data

Divx media format supports metadata in their own format which they call XTAG:
http://en.wikipedia.org/wiki/DivX_Media_Format#DivX_Media_Format_.28DMF.29

However, the newest version of video file editor made by divx now uses
matroska as their container format:
http://labs.divx.com/

Either way, with the divx6 files or with the new matroska container
files you should be able to store metadata in the files.