Hmm. I wasn't trying to recommend privileged or non-privileged mode, just trying to use that to single in on the actual issue.
Alright, if it's just av1, maybe try to use a tool like vainfo
to find the supported codecs. I think ffmpeg fails if an unsupported codec is explicitly specified. But take care if Encoding is mentioned. Some hardware has decoding capabilities only.
It's a complicated topic. And it also took me 2 whole evenings to get the permissions and everything right. I'm using systemd-nspawn, so my experience doesn't directly translate. And it's not any easier than docker.
For video acceleration I found the Arch wiki somewhat helpful. But it's lots of info and not specific to Docker. Maybe it helps anyways: https://wiki.archlinux.org/title/Hardware_video_acceleration
But actually following Jesus' teaching would be way too progressive. As far as I remember he was basically a hippie, advocating for love, helping each other out and the poor, and strongly against hate and capitalism. And he didn't quite like the old traditions. So I think as a christian as of today you definitely need some counterbalance and some other book to point at to defend your conservatism, egoistcal behaviour and hate towards people who aren't 100% like yourself.