While using the website, if I search for Mpeg-4, only h264 (Mpeg-4 AVC and Mpeg-4 Part 10 are also common names for h264) shows up. H.263 can be decoded by Mpeg-4 Part 2 decoders so it is sometimes referred by that as well.

https://github.com/Fyrd/caniuse/blob/master/features-json

Do you manually create the json's or do you have a program/script which does the testing for you? I'm one of the dev for Jellyfin and I maintain this page, I currently do all the testing manually and it's a slow process. Just looking to see how others do things :)
https://jellyfin.org/docs/general/clients/codec-support.html