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A/B Roll

1. An edit which involves two source machines and a record machine. A/B rolls are used when dissolves and other effects between two sources are required. The edit controller manages the control of the two source devices (A and B decks), an SEG (Special Effects Generator) or other device which performs the effect, and the record deck. The effect occurs when the A and B decks are both rolling, and the SEG makes a transition (such as a dissolve, wipe, etc.) from one deck to the other.  Also known as duplex.  2. In Film, a method of negative cutting, producing 2 rolls of equal length, each containing alternative scenes, to facilitate optical effects.


Analog-to-digital conversion.


Audio/Video or Audiovisual. This abbreviation is often found labeling the connectors on consumer equipment.

A/V Hard Disk 

Audio-Video Hard Disk. This is a special type of computer hard disk that is optimized for video and audio capture and playback. It is different from regular computer hard disks in that it maintains the read/write head in the data stream constantly.  Standard computer disks will periodically return the head to the zero track for "recalibration" and can cause dropouts in the audio and video being played. A/V Disks prevent this from happening. 

A/V Server

A system of devices that facilitates recording, storage and playback of A/V material from a RAID or other non-linear devices. 


ATM adaptation layer. The AAL translates digital voice, images and data signals into the ATM cell format and vice versa. Five AALs are defined.

AAL1 supports connection oriented services needing constant bit-rates and specific timing and delay requirements (e.g. DS-3 circuit).

AAL2 supports connection oriented services needing variable bit-rates (e.g. certain video transmission schemes).

AAL3/4 supports both connection less and connection oriented variable rate services.

AAL5 supports connection oriented variable bit-rate data services. Also known as Simple and Efficient Adaptation Layer (SEAL).

 A-Frame Edit

A video edit which starts on the first frame of a 3:2 sequence. The A-frame is the only frame in the sequence where a film frame is completely reproduced on one complete video frame.

 A-Mode Edit

An editing method where the footage is assembled in the final scene order. Scene 1, scene 2, ...


Alternating Current - The method of power transmission used throughout much of the world. The primary characteristic of alternating current is a continuously variable voltage that changes in polarity (positive to negative) at a repeating interval. In the U.S., these changes occur at a rate of 60 cycles per second or 60 Hertz (Hz). AC power standards are strictly regulated in each country and are often used as a point of reference for signal timing and synchronization in electronic circuitry.


See: Dolby Digital

AC Coupled

A technique to remove the constant DC voltage component from an AC signal.

 AatonÆ Code

A form of time code recorded optically along the edge of the film, during its exposure in camera. After development, the code can be read by an optical sensor. Typically used to synch sound during the telecine transfer.


Distortion, usually optical, especially of lenses

Absolute Event

A schedule event whose start time is determined by an assigned time value based on the facility master clock.

Absolute Jitter

The variation in position of a signal’s transitions relative to those of a synchronous stable reference clock.

 Academy Format

A film aspect ratio of 4:3, which is 1.33:1 It is of particular importance because this is also the aspect ratio of standard television systems.

 Academy Leader

A precise length of film (typically 12 or 8 feet) with precise timing, identification and synch information. Provides a numbered countdown (in feet or seconds) to first frame of picture.  


Used to describe the state of an event or device. An active event is one that has been cued or is in preroll, playout or postroll. An active device is one that is responsible for playing an active event.

 Active Video

The portion of a video signal which is visible on a screen, and not blanked. Vertically the active picture area is 487 lines for NTSC and 576 lines for PAL. Also known as Active Picture Area


Advisory Committee on Advanced Television Service.

Access Time

The total time required to find, retrieve, and display information. Access time varies from minutes on a videotape, seconds on videodisc and CD-ROM, to milli-seconds on a computer.

Access Unit

A coded representation of a presentation unit.  I the case of audio, an access unit is the coded representation of an audio frame.  In the case of video, an access unit includes all the coded data for a picture and any stuffing that follow it up to, but not including the start of the next access unit.  If a picture is not preceded by a group_start_code or a sequence_header_code, the access unit begins with the picture start code.  If a picture is preceded by a group_start_code and/or a sequence_header_code, the access unit begins with the first byte of the first of these start codes.  If it is the last picyue preceding a sequence_end_code in the bit stream, all bytes between the last byte of the coded picture and the sequence_end_code (including the sequence_end_code) belong to the access unit.


The process of acquiring video footage. Usually refers to acquiring footage on one format with the intention of performing post-production work from the acquisition format to a higher-quality format.


A software program by Adobe that creates and reads .pdf (portable document format) files.


Used to describe the state of an event or device. An active event is one that has been cued or is in preroll, playout or postroll. An active device is one that is responsible for playing an active event.

Access U nit

A coded representation of a presentation unit.  In the case of audio, an access unit is the coded representation of an audio frame.  In the case of video, an access unit includes all the coded data for a picture and any stuffing that follows it up to but not including the start of the next access unit.  If a picture is not preceded by a group-start-code or a sequence-header-code, the access unit begins with the picture start code.  If a picture is preceded by a group-start-code and/or a sequence-header-code, the access unit begins with the first byte of the first of these start codes.  If it is the last picture preceding a sequence-end-code in the bit stream, all bytes between the last byte of the coded picture and the sequence-end-code (including the sequence-end-code) belong to the access unit.

Active Loop

If the input video signal to a video device is terminated, buffered, amplified and regenerated as an output, then Active loop-through refers to these output connectors.

Active Video (Lines)

Refers to the portion of the video frame that holds the displayable picture information.  In NTSC, 486 lines out of a total of 525 are active; the remainder is used for sync, vertical blanking, etc.

A/D (Analog to Digital) Converter

A device or process used to convert analog signals to digital signals used in TBCs, frame syncs, frame grabber boards, etc. It is achieved by sampling the signal at intervals and then quantifying each sample to give them values suitable for use in a digital system.  Also known as an ADC

Adaptation Field

Ancillary program data (especially PCR) which are uncoded and are transmitted at least every 100 ms after the TS header of a data stream (PID) belonging to a program.  

ADC (A-D, A/D, A-to-D)

Analog to Digital Conversion. Also referred to as digitization or quantization. The conversion of an analog signal into the digital data representation of that signal-normally for subsequent use in a digital machine. For TV, samples of audio and video are taken, the accuracy of the process depending on both the sampling frequency and the resolution of the analog amplitude information-how many bits are used to describe the analog levels. For TV pictures eight or 10-bits are normally used; for sound, 16 or 20-bits are common, and 24-bits are being introduced. The ITU-R 601 standard defines the sampling of video components based on 13.5 MHz, and AES/EBU defines sampling of 44.1 and 48 kHz for audio.
For pictures, the samples are called pixels, each containing data for brightness and color.
See also: Binary, Bit.

Additive Color System

A color system in which an image is reproduced by mixing appropriate amounts of red, green, and blue lights.


The location on the videotape by time code frame number.

Address Track

A track on magnetic tapes dedicated to recording time code or some other means of position identification.


Asymmetric digital subscriber line.  A COFDM-coded digital data stream with a rate up to 1.5 Mbit/sec which is transmitted via telephone lines, mainly for video on demand. A-DSL is a new form of Internet connection rapidly growing in the US.


Adaptive Differential Pulse Code Modulation. A compression algorithm that achieve bit-rate reduction through the use of adaptive prediction and adaptive equalization.


Audio Engineering Society. U.S. based standards and recommended practices organization governing audio technical issues. International Headquarters-60 East 42nd Street, Room 2520, New York, New York 10165-2520. Tel: 212-661-8528. Fax: 212-682-0477. Email: HQ@aes.org . Internet: www.aes.org


The AES Recommended Practice for Digital Audio Engineering - a Serial Transmission Format for Linearly Represented Digital Audio Data. This is a major digital audio standard for serial interface transfer. It is substantially identical to EBU Tech. 3250


The standard for digital audio defined by the Audio Engineering Society and the European Broadcasting Union, now adopted also by ANSI (American National Standards Institute). The standard specifies for professional post production audio, a sample frequency of 48 kHz and a quantizing level of either 16 or 20 bits. Used by most forms of digital audio from CDs to D1.

AGC (Automatic Gain Control)

Circuitry that automatically adjusts the gain level providing optimum signal output and preventing potentially damaging circuit overload. AGC circuits are used in cameras and recording devices, and other video devices to maintain proper signal levels without requiring an operator to manually monitor controls. (See Gain).

ALC (Automatic Level Control)

Similar to AGC, the ALC circuit automatically adjusts the voltage level on camera pick-up tubes to compensate for fluctuations in the level of light on the tube surface.


A plan of the exact sequence of steps needed to accomplish any task. In the compression of video for digital recording or storage, an algorithm is used when the video is decompressed in order to put back the information eliminated during the compression.


A signal with unwanted high-frequency components.


1. Inaccurate rendering of an image due to a low, digital sampling rate. Aliasing appears as jaggies, or jagged edges on graphics and especially text. Aliasing is corrected by special software and techniques (anti-aliasing) which smooth out the jagged edges by anticipating and displaying the interim pixels. In analog CCD systems, a form of distortion that is associated with the process of signal sampling, resulting in stair step edges on diagonal lines within the image. 2. Undesirable effects caused by image detail exceeding the sampling frequencies used. 

For example: 

  • Temporal aliasing - the spokes of a wagon wheel apparently rotating backwards. 
  • Raster Scan aliasing - the twinkling effect on fine horizontal lines, or the jagged edges produced by curved or oblique lines.


The first testing stage of a new program. The alpha stage occurs before a program becomes a beta version.

Alpha Channel

A term used mainly with video graphics systems. The dedicated memory layer, analog signal or digital signal that stores or carries the opacity information of the video. An Alpha Channel video output is available on some systems to enable external video keying.

Alternate Event

Schedule event, determined in advance, which is available to the operator for transmission in place of the originally scheduled event.

Alternate Source

Device or system providing the signal content for a Alternate Event.


“Amplitude Modulation”. A method of encoding data onto a carrier, such that the amplitude of the carrier is proportionate to the data.


Ambient or overall light is directed around rather than at the subject. Ambient noise is background or existing sounds at a location. Ambient air is the sound of a movie set or other location at its normal quiet level, as distinct from absolute silence.

Ambient Light

The normal unaltered lighting conditions of a scene. Ambient would include normal room illumination (indoors) or normal conditions outdoors.



Unit of electrical current flow.  One Amp of current flow is when one Coulomb of electrons (6.25x1018 electrons) passes a given point in one second.


A device that boosts or strengthens a signal.


How large or powerful the signal is, determined by the quantitative value of the signal.

Amplitude Modulation (AM)

A method of imposing intelligence onto a high frequency oscillator wave by varying the amplitude of that wave.  The intelligence can be audio, video or other information.


A signal that is a likeness of or analogous to a physical process and is continuously variable. Analog electronic signals, the basis for conventional video and audio recording and imaging processes, are distinguished from digital signals which represent discrete numerical samples of information—the basis for computer imaging processes.

Analog Recording

The recording of a continuously variable electronic signal. Analog recording is the basis for all conventional (non-digital) audio and video recording techniques. The recorded signal is a duplicate representation of (analogous to) the original signal. Analog recording's major drawback is the introduction of inherent electronic noise to the recorded signal which increases each time the signal is processed or re-recorded.

Analog-to-Digital Conversion (A/D)

The process of converting an analog signal into a digital bit stream. Includes the steps of sampling and quantizing.

Analog Transmision

A type of transmission in which a continuously variable signal encodes an infinite number of values for the information being sent (compare with "digital").

 Analog Video

Video system of continuous variable electrical waves, whose size and shape contain essential picture information. Technically inferior to digital. Picture noise is introduced when tape copies are made. This ‘generation loss’ can lead to unacceptable quality.


A system with different magnification in the horizontal and vertical planes, allowing the recording of wide screen formats. Examples are cinemascope in film, and Pal Plus in video.


A synonym for a hyperlink.

Anchor Frame

A video frame that is used for prediction.  I-frames and P-frames are generally used as anchor frames, but B-frames are never anchor frames.

Angle of View

That portion of a scene visible through a particular lens. Angle of view is determined by the lens focal length. Wide angle lenses have a greater angle of view and, therefore, show a wider area of the subject. Telephoto lenses have a narrow angle of view showing smaller portions or close-ups of the subject.


A roughly animated approximation of a scene or sequence of scenes used for testing an idea and planning a production. Widely used in the advertising industry to make prototypes for client approval.


Single images displayed in rapid sequence producing the illusion of motion.


A way of logging on to servers as a guest, which gives you limited access to that server. Many FTP sites allow you to login anonymously in order to download files. Directories or files requiring a secure User ID and Password will not be accessible.

Answer Print

The first fully graded print, combining picture and sound and submitted by the laboratory for the customers' approval.


Aliasing causes jagged edges in images displayed on a computer screen in low resolution. Anti-aliasing software smoothes the stair-step affect by anticipating and displaying the interim pixels. In analog CCD systems, anti-aliasing is accomplished by the removal of unwanted high-frequency components through the means of a high-frequency-cut optical filter placed before the imager.   Also, a technique that uses the alpha channel to soften the jaggies of generated characters and graphics on video.


American National Standards Institute


The iris opening in a lens that regulates the amount of light passing into the camera. The size of the aperture opening determines the amount of light that will get to the imager. The larger the opening, the more light that enters. Aperture is usually signified in f/stops.

Aperture Correction

The process of enhancing apparent resolution, especially in video cameras, telecines and noise reducers. The technique exaggerates edges. Also known as Contour Correction


Application Programming Interface. A set of interface definitions (functions, subroutines, data structures or class descriptions) which together provide a convienient interface to the functions of a subsystem and which insulate the application from the MIB. A system or application software that provides resources and functions for programmers to create user interface features or provides access to other applications. 

APL (Average Picture Level)

APL is the average signal level during the active picture time, calculated as a percentage of the difference between the blanking and the reference white signal levels.


A small Java- and JavaScript-based Web application. Applets can display animation, perform database queries, or make other Web page enhancements.


A tool used for searching FTP sites for various program files.


  • Deep storage of master material under controlled conditions. 
  • Long term storage of material; especially of material from disk based editing systems, or computer images. 
  • Archive Copy is a master copy intended for storage and not distribution.


Something that shows up as a modification to an original. undesirable elements or defects in a video picture. These may occur naturally in the video process and must be eliminated in order to achieve a high-quality picture. Most common in analog are cross color and cross luminance. An example in digital television would be the observance of blockiness in an MPEG encoded signal or any other impairment that shows up from the original.


Exposure Index or speed rating that denotes the sensitivity for that film emulsion. Defined and named after the American Standards Association, now the American National Standards Institution (ANSI). Actually defined only for black-and-white films, but also used in the trade for color films.


American Standard Code for Information Interchange. A standard code for transmitting data, consisting of 128 letters, numerals, symbols, and special codes each of which is represented by a unique binary number.  An ASCII file is a text file that is in a standard computer readable format understandable to any PC platform.


Asynchronous Serial Interface. A popular interface for digital video broadcasting implementations. It carries the 19.39 Mbps ATSC transport stream within the 270 Mbps ASI format. When the compressed pay load is less than 270 Mbits per second, this format automatically adds null packets to fill out the bit stream and make it a constant bit rate.


Application specific integrated circuit. An integrated circuit designed for special rather than general applications.

Aspect Ratio

The ratio of height over width of an image: a standard video monitor has an aspect ratio of three units of height (vertical) to four units of width (horizontal). This is expressed as a 3:4 aspect ratio. Images will become distorted if forced into a different aspect ratio during enlargement, reductions, or transfers. The aspect ratio for HDTV is 9:16.

As Run Log

Term first used with the Sony Betacart and later the LMS and Flexicart systems.  A merged and filtered document/file the contents of which represent the A/V material that was actually transmitted on a channel or channels by a system over a period of time.

Assemble Editing

A method of electronic editing in which various taped segments are re-taped in a determined sequence to produce a coherent whole. Assemble editing is used to join together larger, pre-edited segments rather than to edit complex, professionally-produced programs.


Lacking synchronization. In video, a signal is asynchronous when its timing differs from that of the system reference signal. A foreign video signal is asynchronous before it is treated by a local frame synchronizer.

Asynchronous S/N Radio

Random noise, 50 dB above the noise floor at fringe of operating range is the FCC requirements.

Asynchronous Transfer Mode (ATM)

A digital signal protocol for efficient transport of both constant rate and busty information in broadband digital networks. The ATM digital stream consists of fixed length packets called “cells,” each containing 53 8-bit bytes-a 5-byte header and a 48-byte information payload.

Aspect Ratio

The ratio of the width of the picture to the height. For most current TVs, this ratio is 4:3. For HDTV, the ratio will be 16:9. The aspect ratio, along with the number of vertical scan lines that make up the image, determines what sample rate should be used to digitize the video signal. Film formats include 1.33:1, 1.66:1, 1.85:1 and 2.4:1.

Assemble Edit

An edit wherein all existing signals on a tape, if any, are replaced with new signals. (See also Insert Edit)


Advanced Television Evaluation Laboratory


Asynchronous transfer mode


Atmosphere. Appropriate background sound to a scene, often added deliberately to cover continuity changes in ambient sound recorded on the day. Atmosphere is also used to describe the impression of an environment, created from a scene or sound.

ATSC (Advanced Television Systems Committee)

The US DTV standard.  There are 18 video formats in this new digitally delivered service.  They range from 480, 720 and 1080 scan lines and can be either interlaced or progressively scanned at 24, 30 or 60 frames per second (fps). 1750 K Street NW, Suite 800, Washington, DC 20006. Tel: 202-828-3130. Fax: 202-828-3131. Email: atsc@atsc.org Internet: www.atsc.org


Advanced Television Test Center


Permission set on a file (such as read/write/execute) to allow certain rights to groups, owners, and public users of that file, i.e. .cgi, .pl, class files.  This is done through a telnet or FTP session.


The U.S. Advanced Television System


Audio Tape Recorder


A physical channel of a digital picture manipulator is attached to a logical channel of a controller if the physical channel is successfully acquired by the controller. A physical channel may be attached to only one logical channel of one controller at a time.

Attack Time

The length of time it takes for a processing device to respond to an input signal.


Attenuation is the reduction of signal strength during transmission. Attenuation is the opposite of amplification, and is normal when a signal is sent from one point to another. If the signal attenuates too much, it becomes unintelligible, which is why most networks require repeaters or amplifiers at regular intervals. Attenuation is measured in decibels.

Audio Dub

1. To re-record the audio portion of a videotape without disturbing the video portion of the signal. 2. To make a copy of an audio tape.

Audio Subsystem

Audio component of a videoconferencing system. The most sophisticated audio subsystems today are full-duplex and employ echo canceller technology. Full duplex allows both sides of a videoconference to hear each other simultaneously without one side being cut off while the other speaks. This provides a more natural and productive environment than less sophisticated subsystems. Echo cancellers insure that audio sent to a remote room is not re-broadcast back to the sender creating an annoying echo effect.

Audio Synchronization Errors (Audio to Video Synchronization)

Audio to video synchronization errors in video systems are usually quite subtle, and are often caused by the buildup of video timing errors from several locations, any one of which will often go unnoticed, but add them all up and you see video arriving annoyingly after you've heard the audio. This gives the appearance of lipsync being off.  It is important to recognize that for even a simple system that audio advances of up to 11 frames can occur and that some of the mismatch actually occurs after the television signal leaves the production environment, and thus can not be seen by the production engineering staff. For more information, go to : http://www.pixelinstruments.tv/4AppNotes/Application%20Notes.htm and/or http://www.pixelinstruments.tv/5ProfesArticles/Professional%20Articles.htm

Authoring System

Specialized computer software which allows users to design interactive courseware in everyday language without the painstaking detail of computer programming.


An event type, which will automatically thread, switch and play an event.

Auto Assemble

An edit in which the off-line edit decision list (EDL) is loaded into the on-line edit computer and all the edits are assembled automatically with little or no human intervention.

 Auto Dynamic Scene Ripple

An option on all da Vinci systems that allows changes made to the scene before a dissolve to be automatically rippled to the next scene (the dissolve).

Auto Iris

A lens iris equipped with a photosensitive detector that can read changes in lighting conditions and automatically open or close the iris to compensate for the changes.

 Auto Scene Detector

A device that detects scene changes based on image content and contrast and then automatically generates an event list. Included as standard in all da Vinci systems.

Automation System

Computers that drive the playout devices, using schedules driven by TCS.


Capability of some digital video equipment to automatically adjust input video timing to match a reference video input. Eliminates the need for manual timing adjustments.


Relating to digital picture manipulation, the X axis is a horizontal line across the center of the screen, the Y axis is a vertical line, and the Z axis is in the third dimension, perpendicular to the X and Y axes, and indicates depth and distance.

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