genlock
The synchronization of two television signals at the vertical, horizontal, and chroma phase levels such that the signals may be cut, mixed, or cross-faded without noticeable roll, jump, or chroma shift.
Note: Modern usage accomplishes this with a frame synchronizer/time base corrector, but it may also be accomplished by a closed loop method or an open loop method, the latter using a pair of rubidium clocks and a video delay line to maintain chroma lock.