We are now offering Shinobi in the official repos. This is a modern and open source NVR written in Node.js. It runs nicely on ARM devices such as RPi4. Enjoy.
Arch Wiki Article: https://wiki.archlinux.org/title/Shinobi
On a RPi4B with 6x cameras each running in 2560x1920 @ 30 fps all in view only mode (no recording) the CPU load over 15 min as reported by uptime or top is only 0.91.