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Video Switching Terminology

The video department as a whole is arguably the most complex of the production department, encompassing all the visual elements. Sitting at the center of all the input sources and output mediums is the video switcher. If you're new to the video department or have aspirations of learning the Switcher position, below is a brief glossary of common terms and acronyms. This is far from an exhaustive compilation, but familiarity with these terms will greatly increase your understanding video as a whole.

3G — A 3 Gbit/s serial digital 10-bit or 12-bit video interface (SMPTE 424M and 425M). AUX (Auxiliary) Bus — AUX buses are extra switching buses that allow video signals connected to the switcher to be routed to external equipment such as VTRs, monitors, projectors, etc. Bank — a name for the three combined individual buses in an M/E, including the PGM bus, the PST bus and the KEY bus. BG (Background) — The switcher bus on an M/E bank that selects the on-line (or on-air) output signal. Chroma Key — A type of key where the hole-cutting information is derived from a color rather than from a video level. An common example on television, is when the weatherman appears to be standing in front of a map. The map itself is a video signal, and the weatherman is in fact standing in front of a green (or blue) screen. On the switcher, the Chroma Key process electronically subtracts the color from the foreground image, and replaces it with video from the background image to form a composite image. Clip, Gain, Opacity — In switcher terminology, the process of fine-tuning a key of any type (luminance, linear, or chroma). Clipping sets the threshold for the hole- cutting circuitry, while "gain" defines the range and sensitivity of adjustment. The "opacity" is the transparency or density of the key, as revealed over a background. Chassis Cards — In addition to the required M/E and System cards, the following cards that can be installed in the chassis, enabling you to configure the switcher in many flexible ways. CLN (Clean Feed) — An output of an M/E that originates upstream of the M/E’s keyers. For example, if the output of M/E 1 is Camera 1 plus a key, the “clean” output is Camera 1 only, minus the key. Computer Video — A generic term indicating video that originates from a computer platform. A progressive scan signal that follows VESA (Video ElectronicsStandards Association) standards, with typical resolutions of 800 x 600, 1024 x 768, 1280 x 1024, etc. Crosspoint — The video switch (or button) that selects the input required on a particular switcher bus. Cut — an instantaneous switch from one video source to another. DA (Distribution Amplifier) — A video device that inputs one video signal, and outputs multiple “identical” signals. DSK (Downstream Keyer) — A DSK is a key that is electronically located after all other switcher functions — visually on top of all other layers and buses. Any operations performed “upstream” on the switcher M/Es will not affect the downstream key video. DVE (Digital Video Effects) — A special effects generator with the ability to create PIP effects, reduce and enlarge images, create borders and shadows around those images, and create keyframes for motion paths.See PIP and Keyframe for additional information. EXT (External) — A digital key input that is dedicated to the DSK. FTB (Fade to Black)— The button which enables the TD (Technical Director) to fade everything on Program, including the DSK, to or from black. GPIO (General Purpose Input/Output) — One or more communications ports that control input and output "triggering." For example, with a GPI (input) trigger, an external peripheral device can trigger a specified switcher function. With a GPO (output) trigger, the switcher can trigger an external device. GUI (Graphical User Interface) — A term that describes a status display based on graphics and icons, rather than strictly on numbers and letters. HD-SDI (High Definition Serial Digital Interface) — a high definition SDI signal (SMPTE 292M). Example formats are 720p, 1080i, and 1080p. Keyframe —In a PIP “move,” a keyframe is a point where an action or change occurs. For example, when a PIP moves from the upper right corner to full screen, keyframe 1 is the upper right position, and keyframe 2 is the full screen position of the PIP. Keying — The process of superimposing video from one source (the foreground) on top of another source (the background). Key Fill — The video which fills the hole cut by the keying circuitry. Typically, switchers provide a variety of choices for the fill source — internal mattes, external video, or "self" fill are several examples. Key Mask — A key modification system that protects a portion of the foreground video from being keyed, using the switcher’s internal pattern system. Key Signal— also known as Key Source. The signal that electronically cuts the hole in the background video signal. Key signals typically originate from external inputs such as character generators or cameras. Linear Key — a keying mode in which the edges of anti-aliased key sources (such as character generators) are reproduced clearly.Typically, two separate signals are required from a linear key source: a cut and a fill.

Control surface and multiviewer screens
control surface and switcher multiviewer screens

M/E (Mix/Effects) — The section (or "bank") of a video switcher where video signals are processed to select inputs and create mixes, wipes, keys and other effects. An M/E is essentially a video layer that can be combined with other M/Es (layers) to form the entire output of the switcher. Menu — A term used to describe buttons and functions on the high-resolution color LCD touch screen. Mix — also known as a Dissolve. A transition between two video sources in which one source fades out as the other fades in. Multiviewer (MVR) — a monitoring system that enables multiple sources (input and outputs) to be displayed on one or two monitors, eliminating the need for individual source monitors. By utilizing different arrays of PIPs, users can select the preferred multiviewer “look,” and streamline control room operations. Native Resolution — The resolution to which all processing is set within the switcher frame, e.g., SD-SDI (SMPTE259M, Level C) or HD-SDI(SMPTE 292M).

NTSC —National Television StandardsCommittee. The oldest standard for color picture broadcasting. NTSC is a standard definition format that operates at a frequency of 60Hz, with 525 lines, 60 fields and 30 frames per second.