Looks like both gphoto2 and ffmepg are available on homebrew, worth giving it a shot for sure. FWIW - I did end up building my own ffmpeg because debian default didn't have NVIDIA support. Want me to give it a try?
Spoke too soon, v4l2loopback-utils is the missing piece on mac. Found this with a basic search[0], if anyone enterprising enough wants to take a crack at it