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A-B Mix See: Crossfade
A/D See: Analog to Digital Converter
AAF Advanced Authoring Format
AC-3 Dolby’s trademark for digital sound system with either 2 or 5.1 channels. AC-3 multi-channel sound provides five completely separate (discrete) channels: Left, Center, Right, Left-Rear and Right-Rear, plus a common Subwoofer channel. The nominal digital bit rate is 384 kilobits per second.
Action Track A digital video effect where fast moving objects appear to remain on screen as a sort of permanent multi-grab. This effect requires motion detection to isolate the moving objects so that they alone can be frozen and accumulated in an overlay image. The technique was developed specially for sports action replay analysis. Synonyms: Image Trail-Freeze
Active Image Active Parts of all Active Lines of the Frame
Active Image Area Area of the display screen, occupied by TV program related picture. Synonyms: Active Picture Area
Active Lines The lines of the TV frame carrying picture information, i.e. all frame lines except the vertical blanking interval. Normally the number of analog active lines is smaller than the number of digital active lines. Synonyms: analog active lines
Active Part The part of the TV line arraying picture information, i.e. equal to the line period minus Horizontal Blanking Interval. Analog Active Part is normally shorter than Digital Active Part. Synonyms: Analog Active Part
Active Picture Area See: Active Image Area
Adaptation A methods of subjective improvement of video processing device performance by dynamic change of hardware settings dependent on the current TV picture content. Adaptation exists in many forms, e.g. long time-constant, frame-by-frame, field-by-field, line-by-line and pixel-by-pixel. Synonyms: Adaption
Adaption See: Adaptation
Adaptive Comb Decoder Decoder with Adaptive Comb Filter
Adaptive Comb Filter A comb filter with Adaptation, i.e. with its response modified by measurement of picture content.
ADC See: Analog to Digital Converter
AES/EBU [Digital Audio Interface] A commonly used digital audio interface specified as a result of co-operation between the Audio Engineering Society and the European Broadcasting Union. It is a serial transmission format for two-channel linearly-represented digital audio data. Each audio sample is carried by a sub-frame containing: 20 bits of sample data, 4 bits of auxiliary data (which may be used to extend the sample to 24 bits), 4 other bits of data and a 4-bit preamble. Two sub-frames make up a frame which contains one sample from each of two audio channels. Frames are further grouped into 192 frame blocks. AES/EBU signal includes channel status data containing information about signal emphasis, sampling frequency, channel mode (stereo, mono, etc.), use of auxiliary bits (extend to 24 bits or other uses), and a CRC (Cyclic Redundancy Code) for error checking. There are several allowed sampling frequencies within the 32kHz to 48kHz range, the most common of which are 44.1kHz and 48kHz.
Alias A form of distortion associated with signal sampling. If samples are taken often enough, the digital signal will be a faithful reproduction of the analog signal. To achieve this, the sampling frequency must be at least twice the highest frequency found in the ‘analog signal being sampled. This minimum sampling frequency is often called the Nyquist frequency. For example, if the highest frequency in the original signal is 2MHz (2 million cycles per second), then the Nyquist frequency is 4MHz (4 million samples per second). If the original signal is sampled at a not high enough rate, e.g. at 3.5MHz, then the digital version will contain not only wanted 2MHz signal, but erroneous signal at 1.5MHz, i.e. artifacts that are not found in the original signal. These erroneous components of the digital signal are called aliases. The resulting signal is then said to contain aliasing. Because of this aliasing it is not more a correct reproduction of the original. Synonyms: Aliasing
Aliasing See: Alias
Analog Active Lines See: Active Lines
Analog Active Part See: Active Part
Analog Component Format Format, where the color difference signals Pr and Pb have exactly the same peak to peak amplitude as the luminance signal Y, i.e. 700mV into 75 Ohm load for 100% saturation. Synonyms: Parallel Analog Interface Format
Analog to Digital Converter - In a narrow sense: A device (usually, a micro-chip) which transforms a signal from analog form to digital form. This is done by taking samples of the analog signal at regular intervals. Each analog sample value is then quantized into a binary code.
- In a wider sense: Device performing all functions, necessary to convert analog video signals to a specified digital interface format, in particular sampling frequency genlocking, video signal pre-filtering, black level clamping, sync code word insertion, and even parallel-to-serial conversion.
Analysis See: TV Analysis
Anamorphic Format Viewed picture format with geometric deformation of the widescreen picture aimed to achieve full vertical screen occupation while using the conventional TV display.
Ancillary Data Non-video data transmitted within video data stream e.g. embedded audio data
Anti-aliasing A filtering process to prevent aliasing or to reduce the aliasing that is already in the signal, i.e. the prefiltering or postfiltering of any data to ensure that they are suitable for the particular sampling structure being used. For instance, smoothing out diagonal lines or curved surfaces in a digitally generated wipe patter, or text from a character generator are particular cases of anti-aliasing. With reference to images it commonly means prevention of "jaggies". Removal of the same artifacts after sampling is usually more difficult and normally involves greater softening of the image. Synonyms: Antialias
Anti-bell [Filter] Filter in a SECAM coder to pre-emphasize the chrominance signal after frequency modulation.
Antialias See: Anti-aliasing
AntiPAL [Test Patter] A test pattern with deliberately wrong PAL switch function: the polarity of V component is not switched and polarity of U component is switched. This pattern enables the measurement of the performance of line averaging function in PAL decoder: when it works correctly, the pattern looks colorless because the AntiPAL test pattern chrominance is canceled by the decoder’s line averager.
Aperture - In general: The smallest elementary Spatio-temporal area addressable by the process of scanning
- With application to filtering: The configuration and weights of taps defining the filter function in spatio-temporal domain
Aperture Correction Horizontal, vertical or two-dimensional processing of video signal with purpose of correcting frequency response distortions or enhance the sharpness of the TV picture Synonyms: Enhancement
APL - Average level of luminance signal within Active Image. Usually expressed as a percentage of Reference White Level
- As a name of test signal: "APL" is often incorrectly used instead of "Flat Field"
Artifact [of a TV Picture] See: TV Picture Artifact
Aspect Ratio The ratio of the width of an object to its height, usually expressed as two numbers separated by a colon, e.g. 4:3, sometimes expressed normalized, with a colon and number one implied, e.g. 1.33.
Aspect Ratio Conversion Conversion of the TV picture geometry preserving the Scanning Standard, e.g. from the so-called anamorphic format to letterbox format. Note that the video signal itself is aspect ratio independent. A CCIR Rec. 601 signal may be either 4:3 or 16:9. Only the display screen has an aspect ratio, thus a "16:9" signal will appear anamorphic on a 4:3 display.
Asset Exploitable Content. Not only is there metadata which identifies what the content is, but there is metadata that identifies who owns it and what can be done with it. This may be as simple as a traditional contract or as rich as a DRM description
Asset Management Identification, copy / transport protection and collation of material essence and metadata
Audio/Video Combiner Device serving to embed several digital audio signals within a digital video signal stream (usually using a serial digital interface).
Auto-phasing A vision mixer with auto-phasing has the ability to compensate for timing differences between its input signals so that it can perform transitions free of shifts. This is usually accomplished by built-in line or frame synchronizers.
Auto-transition A transition (e.g. a mix or wipe) which occurs without the use of a manual control such as a fader arm. Auto-transitions may be triggered from a button on the switcher, or externally in the case of an editor (e.g. via a GPI interface). See: Take
Automatic Chroma Correction See: Automatic Chroma Gain Control
Automatic Chroma Gain Control Automatic correction of chrominance channel gain typically using sub-carrier burst level as a reference. Synonyms: ACC; Automatic Chroma Correction
Aux See: Auxiliary Bus
Auxiliary Bus Some vision mixers have extra switching buses that allow video signals connected to the switcher to be fed to external equipment such as digital effects systems, slo-mo VTR’s, etc. The Auxiliary Bus usually has no specific vision mixer function, it is a utility feature. Synonyms: Aux
Average Picture Level Average level of luminance signal within Active Image. Usually expressed as a percentage of Reference White Level.
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