A vision mixer, also referred to as a video switcher, is a machine that is used to take different sources of video and create a single output. It is most often used in live situations where video broadcasting or recording is being done. In addition to being able to draw from different sources, it can also usually add special effects or mix two or more sources together to form one output. The term video mixer is most prevalent in Europe, whereas in the United States (US) the term for such a device is usually video switcher or production switcher. Vision mixer, video switcher, and production switcher can also refer to the person who operates the machine, although in the US the operator is referred to more often as technical director.
The most common uses of a vision mixer are found in professional video production. This can range from a production studio to a remote truck doing a live broadcast, although more frequently vision mixers are used in live-feed, also called real-time, productions. The mixers range in quality and effects, depending on their use. Video mixers used for remote broadcasts are typically smaller and have fewer capabilities than a larger one used in a production facility.
Vision mixers work in a very similar to how its audio counterpart, the audio mixer, works. They create a master image from several sources and, typically, add some sort of effects, such as a special transition screen between different images. The vision mixer has a variety of types available, but most share some basic components.
The most basic part of a vision mixer is the bus, which contains several buttons that serve to switch between the various signals coming into the device. Typically, a vision mixer will have at least two buses: the program bus and the preview bus. The program bus usually contains the image or images that are being recorded or broadcast, and the preview bus reviews and adds effects to images before they are broadcast. Having a dual bus setup allows for the transitions to be smoother, and it avoids showing any images or footage that is unnecessary.
A vision mixer operator is responsible for manipulating the images and co-coordinating the buses. Most often, this person will receive input from a director as what to do, and when. In many recorded situations where the editing is done after the fact, the effects and mixing are done with a computer rather than with vision mixers.