
Like so much else in tech work, live video production is riddled with jargon. In addition to a series of articles providing in-depth discussion, this space serves to enumerate some of the key terms and concepts you are likely to bump into sooner or later, which may be unfamiliar. Knowledge of these terms will enhance your ability to communicate clearly in this fast-paced industry.
Alpha Channel
This is a mask that defines the transparency portion of an image. When creating graphics for live production, alpha channels obviate the need for keying, and should be used in favor of keying, if supported by your live production switcher or switching software.
Audio Follows Video
Where the audio source is the same as the video source. Typically, audio mixing is handled separately with microphones/audio sources patched into an audio mixer that in turn feeds the live production switcher. However, in some cases, such as playback of prerecorded video, you may want to use the audio channels accompanying the video in the program feed.
CCU
The CCU (camera control unit) is a control box that can be connected to the camera to enable remote calibration or access calibration functions not available through camera’s menu system. This makes aligning multiple cameras in a studio setting much simpler because the change can be made from the control room. CCUs are typically proprietary and parameters that can be adjusted will depend on the CCU model. These parameters may include color balance, black levels, white levels, gain, iris, pedestal, and others.
Chroma Key
This keyer, electronically or with software, replaces a specific hue or limited range of hues with a background image. Green and blue are often used because neither of these hues is present in human skin tone, though any color within the gamut may be used.
Content Delivery Network (CDN)
An Internet-based service that allows viewers to stream live feeds or recordings of your production. Examples include LiveStream, YouTube, Brightcove, and Vimeo. It is important to ensure the device or software from which you are streaming your live broadcast supports a protocol your CDN recognizes. Adobe’s RTMP (Real-Time Messaging Protocol) is one of the most familiar.
Control Surface
Provides the tactile feel of a hardware switcher when using software for live switching or a software-control device, such as a NewTek’s TriCaster series. This often includes a “T-bar” for manually timed transitions. Typically, control surfaces are proprietary and must be compatible with the software or series of software-based switcher you are using.
Downstream Key (DSK)
This is a key applied after “everything else.” It is useful for adding static elements like log bugs and lower thirds, since the logo will remain superimposed “on top of” virtual sets or other composited elements.
See upstream key (USK).
Frame Synchronizer
Provides a buffer that eliminates the need for genlocking video sources. It also enables accommodation of mixed frame rates and sources that are difficult to synchronize, such as HTML or computer signals.
The presence of a frame buffer will delay the video, in some cases perceptibly. For productions where delay is problematic, use a switcher that supports SDI exclusively for inputs and ensure all sources are at the same frame rate. Computer or HDMI sources can be converted separately without introducing a global delay, though additional delay just for these sources will be unavoidable.
Genlock
Genlock (generator locking) synchronizes several video signals such that the next frame (for progressive) or next field (for interlace) starts at the same instant across all sources. Without genlock, cutting between sources that are frame- or field misaligned would produce a visible interruption in the picture. Genlocking requires a common video or sync signal (such as tri-level or black burst) for all sources to lock onto, and each source device (camera or deck) must provide a genlock (sync) input. In a pinch, time-base correctors can be used to reduce sync problems with analog signals.
Digital and software-based switchers very often have frame synchronizers built in, eliminating the need for external sync.
Intercom
A wired or wireless communication system that allows crew members to communicate with each other. In live production, very often intercom and tally will be distributed via the same system.
ISO Recording
ISO, or isolated recording, denotes the ability of a switcher with recording capability to record each incoming channel, as well as the program feed. This is useful if you plan to edit the footage later or for “replay” purposes.
Live Streaming
The online equivalent of a live broadcast. A live feed is continuously uploaded to a CDN for live distribution to viewers.
Luma Key
Keying on a luminance (brightness) value or range of values. Luma key can be more effective than chroma key for certain graphics or where obtaining a good chroma key is difficult. Though any tone can be keyed, in most cases the key will need to be applied to almost pure white or a very dark gray to avoid inadvertently keying out part of the subject or graphic.
Mix/Effects Bus (M/E)
A channel in which you can compose an effect, such as applying a background (keyed-in) element. Some switchers will have several M/E busses, allowing you to create more complex effects, as well as allowing you to keep several pre-composed effects handy.
Multiview
Hardware or software that combines multiple video sources into a single image so that you do not need a dedicated monitor for each source. Modern switchers frequently feature a multiview built in, so you can dedicate one monitor to program and a second to video sources, sometimes with a third for preview.
Preview
Preview is what program will become when you take the next action. Preview allows you to set up effects and otherwise compose the shot before it goes live.
Program
Program is the final image with all effects, keys, overlays, titles, etc., just as viewers are seeing it. Some switchers also feature a “clean” version of the program that excludes certain effects, such as logos and lower thirds. This clean feed can be useful if you want to record the program but potentially overlay different graphics down the road.
Scaling
Video scaling is a transformation that can include a change in resolution and sometimes in aspect ratio of an image (scalers may also feature frame-rate conversion). Scaling is required where one or more input sources do not match the output resolution. Some live production switchers feature built-in scaling capability, and there are stand-alone converters available.
Although scaling may increase the source’s resolution, it does not enhance the image. It simply normalizes the signal’s pixel dimensions to match the switcher’s output.
Scan Conversion
Scan conversion is a special type of video conversion used to convert a computer signal to video or vice versa. A scan converter will likely feature scaling ability; however, for best results when converting a computer signal to a video signal, one should set the output resolution of the computer as close as possible to the target video resolution. Many live production switchers feature built-in VGA or DVI to video scan converters. Increasingly, computers support HDMI output, reducing the requirement for scan conversion.
Talkback
An intercom system that facilitates two-way communication, i.e., the crew can “talk back” to the Director.
Tally
A mechanism for notifying crew/talent when they are live. Most often, this takes the form of a tally light, which may be a stand-alone light or an LED integrated into a piece of equipment, such as a production monitor.
Transition
An alternative to a hard cut when changing camera angles or entering/returning from break. Live production switchers typically offer the basic transitions one finds in video-editing software, such as fades, wipes, and dissolves. More sophisticated transition effects may also be available.
Hardware switchers and control surfaces for software switchers often feature a “T-bar.” This allows you to control the rate of transition manually, or even reverse it. In practice, you may be better served with pre-timed transitions, thereby ensuring consistency.
Upstream Key (USK)
A key applied in a mix/effects bus. This is upstream of the video and any downstream keys. It is used for elements that appear as “part of the shot,” such as virtual sets.
See downstream key (DSK).
Virtual Set
A CG background to give your production a professional, expansive look, even if space or budget won’t allow the construction of a physical set. Virtual sets encompass a range of themes, from news studios to futuristic and period locales. Live switching/streaming software frequently incorporates support for virtual sets. You may be able to create your own virtual sets using 3D composition software.
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