I would go with Jellyfin as a server and Mopidy client as outputs. Like an rpi with an audio hat or class d amp hat. Planning to add Snapcast to the mix for multiroom audio but didn’t find the time yet.
avc1 is the name for H.264 (also called AVC) which is admittedly pretty confusing
MP4box has a great local web tool to test the mime type including the codecs parameter:
https://gpac.github.io/mp4box.js/test/filereader.html
Jake Archibald wrote a good article about this topic: https://jakearchibald.com/2022/html-codecs-parameter-for-av1/
Oh, lousy Smarch weather!
Using a GitHub repository wiki is a low effort / zero cost option. https://docs.github.com/en/communities/documenting-your-project-with-wikis (Clearly not as charming as something self hosted though)