I've not had much experience of docker for less common platforms it seems that multi platform docker builds are a relatively new thing, and that historically most docker platforms have been built for amd64.

I can't find any docker builds for arm on this platform, so I'm building my own.

Current issue seems to be that it can't find the apt installed ffmpeg - will keep you posted.

EDIT: I created a docker image, based loosely on the existing build that was built on aspnet:3.1.12-buster-slim-arm64v8, which already had a compatible ffmpeg. This appeared to work, although there were issues with the audio codec on my camera. I abandoned the docker build as I realised that it was overkill for the job I needed, and I could call ffmpeg in a shell script to do what I wanted.