Depending on your hardware strength and what media you’re converting, the handbrake suggestion might be best. But I’m coming in to say that does take a lot of compute power. You mentioned watching cams, so if it’s popular TV/movie data you’re compressing, it’s often quicker to just download a different, lower resolution source from torrent.

Tdarr

let it watch a folder and it will convert what ever goes in that folder and shove it into a new folder.