Glossary of Audio Visual Terms

Glossary of Audio Visual Terms

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z # 


Access control
A means of protecting computer data from unauthorised access.
Active matrix
A controller which allows the brightness and colour of every pixel on an image.
An Asymmetrical Digital Subscriber Line can transmit at speeds of up to 7Mbps over a single copper pair.
A sequential, step-by-step, problem-solving procedure that can also determine how to decompress data.
Also often known as ‘twittering’, this is a problem associated with interlaced video sources and affects the sharp lines and edges during camera movement, causing objects to shimmer.
Alternate Lighting of Surfaces is a method of achieving high definition and high brightness
Ambient light
The level of lighting present in a room other than the light emitted by a projector.
Analogue signals are the traditional format in which audio and video are transmitted. A digital signal will usually produce a superior video quality.
American National Standards Institute.
ANSI lumens
The degree of lamp brightness, measured in candela.
The hole behind a lens through which light is allowed to pass.
Application Programming Interface is the format used by an application to communicate with an operating system.
Computer software designed for a specific purpose, from sending emails to viewing videos.
Data that has been stored in a format suitable for retrieval on demand.
Advanced Systems Format is a file format which enables digital media data to be streamed over a network. Active Streaming Format is the standard file format of WindowsMediaTM Technologies files.
Aspect ratio
The ratio of width to height of an image.
Asynchronous refers to two or more signals which operate at different rates despite having the same nominal rates. ATM (Asynchronous Transfer Mode) is the CCITT standard for cell relay, where information for multiple types of services, including voice, video and data, is conveyed in small, fixed-size cells. ATM is used in both LAN and Wan environments.
ATM layer
This refers to the layer within the ATM protocol stack for routing and processing activities, including building the ATM header, payload identification, header validation and cell reception, cell routing using CPIs and VCIs, cell multiplexing and de-multiplexing, quality of service specification, prioritisation and flow control.
The loss of signal in a transmission system.
Audio in and out
Connections for external amplifiers and speakers to allow sound output.
Authoring systems 
Entry level software solutions that help users develop interactive multimedia packages, particularly suited to training and education.
Auto balance
Automatic correction of errors in colour balance in black and white areas of an image.
Audio Video Interleave is a digital file format for developing and storing sound and video.
The amount of information that can be transmitted over a network connection, digital connections measure bandwidths in bits per second, Kilobits (Kbps), Megabits (Mbps) and Gigabits (Gbps).
Baud rate
This is the unit of transmission speed equal to the number of times the state or condition of a line changes per second and usual refers to the number of bits transmitted each second.
Short for ‘binary digit’, a bit is a measure of bandwidth.
Bit rate
The number of bits transferred, typically expressed in bits per second, i.e. a file compressed to 28.8Kbps contains 28.8 kilobits of data for each second.
A picture contained on a web page in various formats, including JPG, GIF and TIF.
BNC Connector
A Bayonet Neill Concellman is a connector often used on high end video equipment.
Bits per second.
The Basic Rate Interface converts normal telephone wires into three signalling channels carrying voice and data and are commonly used in high quality ISDN video conferencing systems.
A transmission medium used to transfer high-speed data over long distances.
An area of computer memory reserved for holding and compiling sufficient data to begin streaming.
Built-in loop through
A built-in loop through within a projector enables an additional screen or projector to be connected and display the same signal.

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The high-speed computer memory used to speed up data transfer and store visited web pages temporarily or permanently.
The Constant Bit Rate is a characteristic of a data stream in which the bit rate remains nearly uniform for the duration of the stream. Such traffic requires guaranteed levels of service and throughput.
Computer Graphics Adapter was the first graphics standard for IBM PC-compatible computers and offered a resolution of 320 pixels horizontally by 200 pixels vertically with just 4 colours. It was superseded by EGA (Extended Graphics Adapter).
The chroma, or chrominance, is the characteristics of a picture’s colour saturation and its hue.
A file in a web page or media presentation.
Closed captions
Text, including subtitles, which is added to the video signal. It is referred to as ‘closed’ as it cannot be seen unless the receiving device requests it.
An encoder or decoder is the device through which outgoing video and audio signals are coded and the incoming signals decoded in preparation for playback.
Colour depth
The number of colours that can be displayed by a device i.e. 16-bit colour, 32-bit colour, etc.
Colour temperature
The amount of ‘whiteness’ in a light source, measured in Kelvins.
Combing affects vertical lines during camera movement producing a shimmering effect on interlaced video sources.
Composite video
Composite video is one of the most common AV connections and is the picture signal combined with synchronisation and colour information.
Compressed data uses less bandwidth, saving computer memory space and enabling faster transmission. In display equipment, compression is used to convert resolutions, such as from XGA to SVGA, resulting in a clearer, sharper picture.
The technical specifications of a computer, typically including processor speed, memory, video card type etc.
Connection speed
The maximum rate that data can be transferred, measured in bits per second.
Continuous presence
A split-screen function that allows multiple views to be displayed simultaneously on the same screen.
Contrast ratio
The ratio of darkness to brightness of a scene. A contrast ratio of 400:1 relates to the lumen output of a projected white image being 400 times larger that the projected black image.
The three primary colours (red, green and blue) are used to produce all colours. All three are converged to produce ‘white’.
Cathode Ray Tube.

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Information, including text, nubers, sounds and pictures that can be processed by a computer.
Data compression
Through data compression, unnecessary information can be removed from a data file to save space.
The basic unit of data passed through TCP/IP environments.
Directional Correlation Deinterlacing is a technology which can eliminate jagged edges from moving video.
Data Communications Equipment represents a device, typically a modem, which can manage a session on a network.
Compressed audio and video content can be decoded to a specified digital format, for example MPEG.
Degaussing removes the magnetic field that builds up within CRT monitors.
Desktop video conferencing
Personal video conferencing run on a smaller scale on a desktop model, suitable for individual use or within small workgroups.
This is a mirror or lens that reflects or refracts wavelengths of light and separates the white light source into red, green, and blue light.
Digital Keystone Adjustment
This adjusts and corrects the keystone on a projected image, i.e. to produce a perfect, square-shaped image.
Digital media
Images, sound, text and videos in a digital format that can be downloaded or streamed across the internet and networks.
Digital signal
Digital signals can be transmitted faster than analogue signals and represent a more accurate transmission of computer information.
Digital zoom
This function enables the zooming in and out of images quickly whilst retaining picture quality.
Direct Image Light Amplification is a technology patented by Hughes-JVC designed to improve the light output and contrast ratio of LCD screens.
Distribution amplifier
This allows a source signal to be amplified and distributed through multiple outputs over long distances.
Dithering occurs when a monitor tries to display images specified with more colours than it can handle.
Digital Light Processing is a recent development by Texas Instruments which uses mirrors to display an image. DLP is superior to LCD and is used in most low to mid- range projectors.
Domain Name System refers to the name resolution system that allows users to locate computers on a Unix network or the Internet (TCP/IP network) by domain name. The DNS server maintains a database of domain names and their IP addresses.
The transfer of files to a computer and the method of installation of software from a website.
Dots per Inch refers to the number of pixels in a single inch line.
Digital Rights Management is the technology which maintains the protection of digital content through encryption.
Digital Subscriber Lines is the term for the high-speed, Internet telecommunications line that offers faster download speeds than a 56k modem and provides 24/7 internet connection.
Data Terminal Equipment is the area of the terminal that acts as a data source or data sink and interfaces with the communications circuit.
Digital Video Disc is the latest format for optical storage media with several times the capacity of Compact Discs (CD).
Digital visual interface represents the interface between projectors and computers through a digital connection, resulting in a clearer image than that produced through an analogue connection.
Dynamic Data Exchange (DDE)
DDE is a technology for communication between multiple applications under Microsoft Windows or OS/2. Its primary function is to enable Windows applications to share data.
Echo cancellation
The built-in process which eliminates any acoustic echo in a video conferencing environment
Eco-Mode Technology
A money-saving, highly efficient feature that doubles lamp life and produces a quieter operation.
Enhanced Graphics Adapter offered a display resolution of up to 640 pixels horizontally by 350 pixels vertically and 16 colours from a palette of 64. It was superseded by VGA (Video Graphics Array).
Embedded player
A media player located within a browser window so that only the media clip shows. RealPlayer is a popular media player.
The conversion of audio and/or video content to a specified digital format, including MPEG, by an encoder.
This is a baseband LAN specification that operates at 10Mbps.
The formats for communicating between video conferencing systems.
Hardware and/or software which prevents unauthorised access to private networks.
Graphics software that relies on less bandwidth than traditional video.
The continual rapid increase and decrease of audio pitch due to non-uniform linear speed of an analogue tape.
Focal length
This is the distance from the surface of a lens to its focal point.
A projector’s focus defines minimum and maximum projection distances. Most projectors have both auto and manual focus functionality.
Foot Lamberts
The measurement of reflected light from a surface.
The different ways that information is stored on a program or device, i.e. VHS, DVD, PDF and MPEG.
The series of images that produce video and the frame rate is the number of video frames displayed per second.
The aperture of a lens.
File Transfer Protocol is an internet protocol which enables users to transfer files over a network.
Full duplex
Two way audio which is simultaneously sent and received without interference or ‘clipping’ and is a common feature of video conferencing.
Full motion video
Real time video which is equivalent to broadcast television quality with a frame rate of 30 fps.
A network point that acts as an entrance to another network and a router or computer that converts protocols between different types of applications or networks.
A trail left by a moving object on a slow LCD panel.
Graphics Interchange Format is a graphics format in which images are made up of pixels and can be downloaded quickly.
The Group of Pictures parameters are a trade-off between quality, bandwidth, delay and sensitivity to transmission error.
Anything that appears on a web page which is not text.
H.239 defines rules and messages on how to establish an additional video channel that can be used e.g. to show a laptop's desktop as video or video from a second camera during a video conference.
A compression standard and an advanced protocol that is increasingly being used to control multipoint video conferences and enable a wide range of video conferencing systems to communicate, particularly in ‘chair mode’.
A video compression standard that supports video conferencing and video telephony applications. The H.264 codec has a broad range of applications for compressed video, including low bit-rate Internet streaming and HDTV broadcasting with almost lossless coding.
A widely-used compression standard used to control multipoint video conferences and enable a wide range of video conferencing systems to communicate, usually associated with ISDN.
A rapidly-growing video compression standard that enables video conferencing systems to communicate through the Internet using Internet Protocols (IP).
A less popular video compression standard that relies on the regular POTS (plain old telephone service) to video conference.
A relatively new video compression standard that provides ‘light directory access protocol’ (LDAP) object class specification. It is designed to store and locate video and voice over Internet Protocol (VoIP) information in enterprise directories.
Data which is transmitted in either direction, one at a time so that only one site can speak at a time.
A light source used in projectors.
High Definition Compatible Digital is a patented encoding/decoding process which improves the quality of digital audio recording and playback.
High-Definition Multimedia Interface is the new standard for video interfacing with a bandwidth of up to 5Gbs. It can easily support all current HDTV standards and is backwards compatible with DVI.
The standard for consumer devices which improve compatibility between computers, CD and DVD players.
Horizontal/vertical lens shift
The feature of a projector which facilitates precise image positioning for fast installation and usage.
The computer which provides documents to users and functions as the beginning and end points for transfer of data.
Hypertext Markup Language is the standardised language of the web and is embedded in all web documents.
Hypertext Transfer Protocol is the internet protocol used to deliver information over the web.

A single colour disregarding brightness or luminance.

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Internet Control Message Protocol uses datagrams to report transmission errors between the host and gateway.
In a video compression, this is a frame which is complete and must be located in order to begin playback.
Internet Group Management Protocol is a multicasting protocol used by IP hosts to report their host group membership to neighbouring routers. In v2 ‘leave messages’ features have been added.
The connection between different elements of a system. In software an interface refers to the software a computer runs to enable the user to interact with it.
Interlaced video
The integrated image which the eye sees when the image from video’s two fields are delivered to a video device such as a television.
Internet Protocol (IP)
These protocols are used to communicate across interconnected networks and can be used for common applications such as e-mail, terminal emulation and file transfer.
An internal computer communications network.
In Plane Switching or Super-In Plane Switching is a specific TFT technology in which offers greater viewing angles and contrast ratio.
Integrated Services Digital Network is the recommendation published by CCITT for private or public digital telephone networks. In ISDN transmission, binary data passes over the same digital network that carries common telephone transmissions and is usually faster than a modem.
Internet Streaming Media Alliance represents the industry leaders who are aiming to accelerate the adoption and deployment of open standards for streaming rich media content.
The term used when all devices in a network derive their timing signal directly or indirectly from the same primary reference clock.
Internet Service Provider is the organisation which sells connections to the internet; a user requires an account before access to the internet can be achieved.
A network-oriented programming language designed for writing programs to be downloaded through the internet.
The programming language developed to help make web pages more interactive.
Jitter is the distortion caused by signal variation in analogue communication lines and can cause data loss.
Joint Photographic Experts Group is a compression technique for still images that reduces them to a small percentage of their original file size.
Key frame
A video frame that contains all the data required to produce an image without any reference to the previous frames.
The angle created when an image is projected can slightly distort the shape of the image. Keystoning is a projector feature that corrects the shape by creating a uniform image, top to bottom.
A word or phrase typed into a browser to start an online search.
Most Local Area Networks are confined to one or more buildings and are used to connect workstations, printers and other similar devices. LANs provide access to data and device anywhere on the LAN which can be shared by other users. A system of connected LANs is known as a Wide-Area Network (WAN).
The delay that occurs during the time that a device processes and delivers data.
Liquid Crystal Displays. LCD technology uses three glass panels which sandwich crystals and separate the colour spectrum into red, green and blue. When light is passed through the panels an image is created on the screen.
Lightweight Directory Access Protocol is used to access a listing in a directory.
Lip sync error
This occurs when picture and sounds are not synchronised in time when playing video.
Load balancing
This term refers to the ability of the router to distribute traffic over all network ports that are the same distance from the destination address. It increases use of the network segments and increase the effective network bandwidth.
Local playback
A file that exists on the same computer device as opposed to one stored on an external source such as the internet.
Lossless compression
The process of compressing data in which information is arranged more concisely and restored to its original state upon decompression.
A lumen is a measurement of light. The higher the lumen count is the brighter the projection will be.
The colour intensity of an image.
M1 Connection
A display interface system developed for digital displays that can carry DVI, VGA, USB and Firewire.
MAC address
A Media Access Control address is a hard-coded interface identification used by layer 2 devices (switch or bridge) for proper forwarding of frames between computers on a network.
Maximum resolution
The maximum resolution a monitor can run at.
Multiple Bit Rate occurs when data stream content is encoded at different bit rates to optimise content delivery.
Multipoint Conference Unit systems allow users to connect multiple audio and video sites together simultaneously.
The amount of data that a computer can store on a disk or chip.
Detailed information about data.
Metal Halide
Metal halide lamps are used in most projectors and give a brighter image and last longer than halogen.
Management Information Database.
Microperforated screen
A screen which can have a speaker mounted to the rear of it.
Musical Instrument Digital Interface is a specification which defines a protocol for describing music data.
Micro Lens Array increases the fill factor on LCD panels and reduces the visibility of the pixel grid to almost zero so that the rows and columns of pixels cannot be seen when viewing from a comfortable distance.
The Microsoft Media Server protocol is used to deliver content as a unicast stream.
Mouse emulator
The remote control on a projector usually features a mouse emulator enables the user to move around during a presentation whilst retaining control of the computer source.
MPEG Audio Layer-3 is the audio compression standard.
Moving Picture Experts Group is a type of audio or video file.
A rule created to reduce the emissions of a monitor while working to safeguard the health of computer users.
A method of delivering content via a single stream which is transmitted from a media server to multiple clients who have no connection with the server.
Multicast address
A class D address for multi-network devices.
Multichannel audio
An audio reproduction system that processes numerous sound channels.
A presentation of a range of media, including graphics, animation, sound, video and text.
In computing, this is where a signal is divided into several parts. In video conferencing, this is the combination of two or more signals from two or more channels into a single output. Those multiple channels must be multiplexed or de-multiplexed with a Network Terminating device and are usually built into video conferencing systems.
Multipoint Control Unit (MCU)
Also referred to as a bridge, this is a device that manages video conferences involving three or more participants.
Multipoint video conference
A video conference involving more than two sites.
Multi-Domain Vertical Alignment is a TFT technology, where each sub-pixel is divided into four regions where the liquid crystal molecules are at angles to each other resulting in wider viewing angles and faster video response than TN or IPS.
A low-capacity communications circuit.
Native resolution
A feature of LCD technology, this is the number of pixels that make up the display.
Two or more computers link together to form a network.
The National Television Standards Committee is the video transmission system used in the US, Canada and Japan.
Instant access, when required, to archived or stored content.
The On Screen Display is the menu that enables the user to access and adjust a monitor’s settings, including brightness, image position and colour saturation.
Occurs where computers overlay text and graphics onto images.
Overscanning occurs where the area of a video picture falls outside the viewable area of the display device.
Packet switching
Messages are divided into packets prior to sending and can follow different routes to a destination but are recompiled on delivery.
Phase Alternating Line is the standard for scanning television signals and is used in the majority of European countries.
Participant map
A visual map which shows where the participants of a video conference are sitting.
Portable Document Format was developed by Adobe Systems to capture and deliver most document types without changing the format or recreating it within another application. Acrobat Reader is required to view a PDF document.
This term refers to the difference between the complete subject frame and its predecessor in video compression environments. It represents the most compact amount of data needed to generate the subject frame given the preceding complete frame but does not allow reverse single step or playback.
An organic material that produces light when stimulated by the electron gun in the CRT.
The curve seen in an otherwise straight line at the sides of some displays (particularly CRT).
PIP (Picture-in-Picture)
The ability to project a secondary image (from another source such as a DVD, VCR or PC) within the main projection image.
A small dot which represents a single element of a display. The more pixels an image has, the more defined the image will appear to the viewer.
Pixel frequency
The amount of pixels that can be displayed on a monitor per second e.g. 110MHz.
If compression by DVD and digital channels is not performed with care, the image looks rougher and coarser than it should, with a grainy effect over parts of the picture.
Plasma display
A plasma display is a video display in which each pixel on the screen is illuminated by a tiny bit of charged gas. Plasma displays are thinner than cathode ray tube (CRT) displays and brighter than liquid crystal displays (LCD). Plasma displays can be used to display either analogue video signals or digital computer input.
Platform refers to both a computer operating system, i.e. Windows, Mcintosh, Linux and to the actual computer hardware, i.e. Mcintosh or PC.
A list of digital media content.
Picture Line Up Generation Equipment is the test pattern developed by the BBC to help set black levels in a video picture correctly.
Software that extends the capabilities on a computer, for example to watch moves or access animation.
Point-to-point video conference
A video conference between two sites.
A material used in the manufacturing of LCD displays which results in a superior contrast ratio and quicker response time than TFT LCD screens.
Portable device
A mobile electronic device, such as a pocket PC, digital music player or Smartphone, which can exchange files or data with a computer or other device.
A website that acts as a starting point to other areas of the web.
An effect which occurs when a smooth colour transition instead appears as irregular steps in colour.
An electronic device that increases a signal’s output level to match the signal input level of another device.
Presentation mode
Also referred to as broadcast or lecture mode, presentation mode enables a single location to be viewed and heard during a conference by all participants.
Progressive scan
Progressive displays can show progressive scanned images as opposed to interlaced and have the ability to draw every line of the projected image resulting in a clearer and more defined image.
Proprietary compression algorithm
An algorithm for the compression of a video signal. Video conferencing systems using this algorithm are only able to communicate with a remote site using the same algorithm, which is why many vendors use only standard compression algorithms to facilitate communication across their platforms.
A set of procedures and formats than enables computers to exchange data.
Protocol rollover
A procedure that enables switching from one protocol to another when a Windows Media service fails to make a connection using a specific protocol.
Proxy server
A server on a network between client software and another service that intercepts requests to the server, forwarding to other servers if necessary.
Public room
A video conferencing service offered for public use.
Public switched telephone network (PSTN)
A domestic telecommunications network that is usually access by telephones, telephone systems, private branch exchange trunks and data arrangements.
Publishing point
A virtual directory that stores content or delivers a live stream in the Microsoft Windows Media environment.
The method of delivering data to a client only on the client’s request.
The method of delivering data to a client without the client’s request.
Patterned Vertical Alignment is the TFT-LCD panel technology patented by Samsung giving superior viewing angles and a high contrast level.
Quality of Service is the term for a set of parameters and their values that determine the performance of a virtual circuit.
Software that enables the user to view a range of digital media, including video, sound, animation, music, text graphics etc.
Redundant Array of Independent Disks is a multi-drive storage facility providing high performance and redundant hardware with protection against failure.
Rainbow effect
On DLP projectors, the inability of the DLP colour wheels to refresh pixels fast enough results in colour separation on the edges of fast-moving objects and is known as the rainbow effect. Some viewers are more prone than others to seeing the rainbow effect.
Random Access Memory is the computer hardware used for the short-term storage of data.
A connector used commonly on audio visual equipment.
Real time
The actual time that an event takes place.
Rear Screen Projection
The projector is positioned within a large cabinet, supporting an opaque screen and projects its image onto the screen from behind. Most projectors have the ability to mirror the image they produce in order to work within a rear projection cabinet.
Recommended resolution
The recommended resolution a monitor can run at.
Refresh rate
The rate at which a CRT monitor redraws an image; a refresh rate of 85Hz or higher is considered flicker-free.
The clarity or sharpness of a picture described in dots per inch (dpi).
Response time
A term associated with LCD technology, this is the time an individual pixel takes to turn fully on then off. There is a rising (r) and falling (f) time which gives the overall figure.
Red, green and blue are the colours that, when combined, comprise all the colours on a computer screen.
RMS watts
The average maximum power output of an amplifier or the maximum average power of a speaker which is measured at 0.1% THD (Total Harmonic Distortion).
Room-based video conferencing
Video conferencing that uses a large, sophisticated system as opposed to desktop video conferencing.
A dedicated computer hardware or software package that manages the connection between networks.
Real-time Transport Protocol is the internet protocol which delivers real-time audio and video streams over unicast or multicast networks.
Real-Time Streaming Protocol establishes and controls either a single or multiple synchronised streaming of continuous media. It provides a framework to enable controlled, on-demand delivery of real-time data.
Synchronised Accessible Media Interchange is an XML-based language for specifying closed captions in languages and styles.
The process of converting an analogue entity to digital form.
Session Announcement Protocol announces the presence of a device on a network.
The strength or purity of a colour present within a television image.
A device that deinterlaces an image, then scales it to the native resolution of the output device. It can significantly enhance picture quality, particularly on plasma screens and projectors.
Scan converter
In a projector, this converts a digital signal from a computer to a video signal for broadcast on a video projector or TV monitor.
Screen gain
The extent to which a projection screen can make an image appear brighter.
Small Computer System Interface is a hardware interface that enables the connection of up to 15 devices to a single PCI board, or SCSI host adaptor which then connects to the motherboard.
Serial Digital Interface is the standard used in broadcast and high end video systems for transmitting digital component video over a coaxial cable.
Session Description Protocol is the multicast configuration file for MPEG-4 audio, video and network settings.
A 625 line, 50 interlaced field per second analogue broadcast standard, Sequentiel Coulcur a Memoire is the French television standard, also used in Russia.
A computer that provides a service to client software that runs on other computers.
Set-top box
A less expensive unit that replaces a destination decoder and streams to a television set.
Shadow Mask
The most widely available CRT technology in which a perforated sheet of metal acts as a filter behind the screen to channel electron beams to corresponding phosphors. It has greater definition in smaller areas, superior colour definition and is a less expensive technology.
Short throw lens
These lenses are designed to project a large image from a short distance and most projectors are equipped with them.
Super High Pressure Lamps.
A user interface than customises the appearance and functionality of software.
Synchronised Multimedia Integration Language enables website creators define and synchronise multimedia events for presentation and interaction.
Simple Network Management Protocol is the internet network management protocol which can monitor and set network configuration and runtime parameters.
Sound card
A circuit or expansion board that adds audio functionality to a computer.
Standardized Red, Green, Blue is the colour space defined by Microsoft and Hewlett-Packard to match colour between applications and hardware devices such as monitors, scanners, printers, and digital cameras.
Secure Shell software provides secure logon for Windows and Unix clients and servers.
Standard compression algorithm
A convention for the compression of a video signal.
Live, real-time transfer of digital information, including audio, video and multimedia over networks and the internet on demand and in a continuous flow, i.e. it is played by client software as it is received. Streaming files match the encoded bit rate to the connection speed of the user so that remote viewers can play media with minimal stoppage and without first downloading an entire video file.
Sub pixel
A pixel is made up of three same-sized, red, green and blue cells which produce the colour emitted by a display.
Subnet mask
This is used to group IP addresses together, commonly used by routers to define the group to which an IP address belongs in order to identify the correct interface from which it should forward the IP packet.
Super Video Graphics Array refers to a display resolution of 800 pixels horizontally by 600 pixels vertically. This is currently the lowest projector resolution on the market.
Super video is the signal transmitted as two sub-signals requiring two wires – luminance (Y) and colour (C) and can only represent standard definition interlaced video signals
Switched digital communications
Digital communications which allow the user to dial up another user on the public network as opposed to a dedicated, point-to-point connection.
The process of maintaining digital media files on a portable device such as an MP3 player.
Circuits operate at the same speed are said to be synchronous.
The standard for real-time data conferencing which defines interfaces with whiteboards and application viewing and sharing.
Also referred to as Digital Signal Level 1 (D1), this is a digital transmission functionality operating with a nominal bandwidth of 1.544 Mbps and usually composed of 24 DS-0 channels. It is the primary digital communication system of North America.
Also referred to as D3, this is a digital transmission functionality operating at 45Mbps bandwidth and usually composed of 28 DS-1 channels.
The acronym of the Swedish Confederation of Professional Employees that has set stringent standards for devices that emit radiation.
Transmission Control Protocol is the protocol of TCP/IP which governs the break-up of data messages into packets to be sent through IP and the reassembly and verification of the complete messages from packets received by IP.
Transmission Control Protocol/Internet Protocol is the common name for the suite of protocols developed by the American Department of Defense in the 1970s to support the development of international inter-networks.
Television from cinema is the system used to transcribe movie film content onto electronic media.
Thin Film Transfer offers more efficient use of the light source that creates the image from LCD panels.
Three panel LCD
Projectors using one panel for each primary colour offer enhanced colour reproduction and a richer image.
Throw distance
This is the distance from the centre of a projector lens to the centre of the screen onto which it is projecting.
This is a small version of a page or image that provides a simple method of browsing multiple images.
Tagged Information File format is a graphic file format for still images or bitmaps in web pages.
The largest unit of content of a DVD, such as a movie, is called a title although there is no consistent standard across DVDs so more than one title can be included.
Twisted Nematic is a specific, mature type of TFT technology in which the alignment surface, and therefore the liquid crystal molecules, is orientated 90 degrees from each surface of glass.
An internet utility that describes the path in real time from a user’s machine to a remote host and reports the IP address of all routers in between the two.
A song or similar piece of audio content.
An error test for a condition in a running machine which can identify the condition and provide a recovery route for it.
In an interlaced picture each frame is made up of 2 fields. When field 1 is created odd scan lines are drawn and when field 1 is complete field 2 is created which results in an interlaced picture. The horizontal line that moves from the top of the screen to the bottom is at a different position when field 1 is drawn to that of field 2 and the resulting flicker which can be seen at the edges of each line is referred to as a twitter.
User Datagram Protocol is a connectionless transport protocol within the TCP/IP stack and is used in cases where some packet loss is acceptable.
Ultra High Efficiency is the term typically used with metal halide lamps.
The method used by media servers to provide content to connected clients who each receive a discrete stream and where no other client has access to that stream.
Uniform Resource Identifier (URI)
A compact string of characters used to identify or name a resource. The main purpose of this identification is to enable interaction with representations of the resource over a network using specific protocols.
To transfer data from one computer to another and the opposite of download.
The Uniform Resource Locator is a unique identifier which describes the location, or ‘address’ of a piece of information or document, including the protocol used to access that information.
Ultra eXtended Graphics Array refers to a display resolution of 1600 pixels horizontally by 1200 pixels vertically, usually only required in specialist applications.

Variable Bit Rate varies from second to second and is the two-pass encoded process that analyses and compresses movies to an optimal, rather than uniform, data rate.
A video CD is a compact disc format that contains ISO MPEG-1 compressed full motion video and high quality audio.
Vector graphics
These are programs which store images using computer algorithms to define shape, lines, animation etc.
The airflow through a projector’s internal components which acts as a cooler for the lamp or light source.
Vertical frequency
The rate per second, measured in Hertz (Hz), that the monitor draws all the lines on an entire screen and the higher the frequency the less a flicker is produced.
Video Graphics Array refers to the video display resolution standard of 640 pixels horizontally by 480 pixels vertically with up to 16 colours at a time and also allows for 320x200 resolution with 256 colours. Video Graphics Array use RGB data to transfer data.
Video bridge
A computerised switching system, or MCU, which allows multipoint video conferencing.
Video capture
The method of capturing an analogue video source and converting it into a digital format.
Video conferencing
A personal communication mechanism with audio and video content that can include graphics and data exchange.
A graphics display that changes in response to an audio signal transmitted within Windows Media Player.
VoD server
Video on Demand refers to any streaming video server that can store and deliver video streams on request from end users.
Voice-Activated Switching
VAS is usually the default mode in multiple sites where the personal currently speaking can be viewed by all participants. Noise in a site will cause the view to change.
Volume levelling
The automatic increasing or decreasing of volume during playback to produce a similar sound for all audio content.
Virtual Private Network is a service offered by public carriers whereby the user is given a network that appears to be private but which is actually carried over a public network.
A Wide Area Network is a communications network that uses devices such as telephone lines, satellite dishes, or radio waves to span a larger geographic area than can be covered by a LAN. The Internet is a WAN.
This is a format for a digital audio sound file.
Web server
A server that stores and retrieves HTML document and other resources using HTTP.
The delivery of a live or recorded broadcast over the web.
A user-friendly help file that guides the user through computer processes, applications and programs.
Windows MetaFile is the standard introduced by Microsoft for the exchange of images between Windows applications with the functionality to store a screen image along with the vector information needed to recreate it in a single file.
Wide Extended Graphics Array refers to the widescreen display resolution of 1366 horizontal pixels by 768 vertical pixels with an aspect ratio of 16:9, popular for LCD and plasma flat panel displays. Computer displays refer to a WXGA resolution of 1280x800 pixels with an aspect ratio of 16:10.
Extended Graphics Array refers to a display resolution of 1024 pixels horizontally by 768 pixels vertically.
A cable or adaptor that enables a single output into two inputs or a single input into two outputs.
Compression technology that compresses large files, such as graphics to other users over the internet. After the Zip file is downloaded, a decompression software program is required to ‘unzip’ the document.
Zoom lens
A projector lens that allows the adjustment of focal length (image distance compared with size) without physically moving the projector.
Zoom ratio
This is the ratio between the smallest and largest image a lens can project from a fixed distance. A zoom lens is not as ‘bright’ as a fixed lens and the higher its ratio, the less light output is emitted.
15 Pin D-Sub
A connector for a PC’s VGA port or analogue monitor.
2.2 pull down
This refers to the electronics required to convert film footage to PAL and SECAM video format.
3.2 pull down
This refers to the electronics required to convert film footage to NTSC video format.
4:3/16:9 dual format

This dual format enables the viewer to switch between alternative picture formats in traditional square or wide-screen views.

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