Scaler vs Switcher

A scaler and a switcher are two different devices that are often confused. A scaler converts an incoming signal to a fixed output resolution and frame rate, so that sources in different formats can feed the same display. A production switcher (vision mixer) selects between several sources and performs transitions such as cuts, dissolves and wipes; it expects synchronised sources in the same format, either genlocked or realigned by frame synchronisers on its inputs. A presentation switcher, or seamless switcher, combines both functions: it scales every input to a common output format, then switches between them without a visible break. Switching between unsynchronised sources without scaling or frame synchronisation produces a glitch at each transition.