What is genlock and do you need it?

Genlock (generator locking) makes several video devices run from one shared timing reference, so that every device starts each frame at the same instant. Their outputs can then be cut between, mixed or layered cleanly. You need it for traditional hardware switching of several cameras. You generally do not need it for single-camera streaming or recording, or for software and NDI-based production.

Without genlock, two cameras (or a camera and a graphics system) each run from their own internal clock, fractionally out of step with one another. On a single source that is invisible. When a mixer cuts or layers sources that are not locked together, the new source’s frame does not start at the same instant as the old one, and the result can be a visible tear or glitch at the cut. A reference signal fed to every device removes the problem at source. Many modern mixers solve it another way, with a frame synchroniser on each input that re-times the incoming signal.

Genlock matters in live multi-camera production where sources are switched or layered in real time through equipment that expects locked inputs: studio production, live sport, multi-camera events and virtual sets. It generally does not matter for single-source recording or streaming. It is also not used in IP-based NDI workflows or software switchers, where the receiving software aligns the frames as they arrive and no dedicated reference signal is involved.