I'd probably go for a small N100 mini-PC.
Should be plenty powerful for what you need, very low wattage and relatively trivial to get GPU pass through in Proxmox. Alternatively one of the more powerful versions.
This depends on how many cameras, resolution and frequency of course, but you should be able to see if others with similar setups have it running smoothly. You'd be limited on storage, but can set up NFS to your NAS or existing server.