What is a Vision mixer?
A vision mixer (also called video switcher, video mixer or production switcher) is a device used to select between several different video sources and in some cases composite (mix) video sources together and add special effects. This is similar to what a mixing console does for audio.
The main purpose of a vision mixer is to create a master output for a real-time video recording or broadcast. Typically vision mixers are used for live events, or any event where multiple sources need to be mixed in real-time. Vision mixers can also be used to create various visual effects, from simple mixes and wipes between sources to advanced composite effects.
The main concept of a professional vision mixer is the bus, basically a row of buttons with each button representing a video source. Pressing such a button will select the video out of that bus.
As a job, vision mixers are technicians who work at a console in the gallery or studio control room. They are responsible for controlling the vision mixing desk: the pictures viewers see on their television are the result of the work of the vision mixer.