Synchronization of vertical phase of video signals in a video system

A video system in which synchronization of the vertical phase components of a plurality of video signals is carried out by a plurality of reference signals having substantially the same frequency and substantially a fixed relative phase relationship. Each vertical synchronization signal is locked to one of the reference signals at a phase associated with the measured phase difference between the vertical synchronization signal and a selected one of the reference signals. In this way, all the vertical synchronization signals are brought into phase with one another.