AAC Advanced Audio Coding, a codec originally known as MPEG-2 NBC (non-backwards compatible), is considered the successor to MP3, with about 25 percent efficiency improvement. However this performance has more recently been considerably enhanced with aacPlus, also known as High Efficiency AAC (HE-AAC), and included in MPEG-4 and delivers CD quality stereo at 48 kb/s and 5.1 surround sound at 128 kb/s. Websites: (AAC) www.audiocoding.com, (aacPlus) www.codingtechnologies.com
AAF The Advanced Authoring Format - an industry initiative, launched in 1998, to create a file interchange standard for the easy sharing of media data and metadata among digital production tools and content creation applications, regardless of platform. It includes EBU/SMPTE metadata and management of pluggable effects and codecs. It allows open connections between equipment where video, audio and metadata, including information on how the content is composed, where it came from, etc., are transferred. It can fulfill the role of an all-embracing EDL or offer the basis for a media archive that any AAF-enabled system can use. In 2007 AAF Association, Inc. changed its name to Advanced Media Workflow Association (AMWA), with direction and focus on file-based workflows including AAF, MXF and other formats Website: www.aafassociation.org
AB Axis (x, y, z) Used to describe the three-dimensional axes set at right angles to each other, available in DVE manipulations. At normal x lies across the screen left to right, y up the screen bottom to top and z points into the screen. Depending on the power of the equipment and the complexity of the DVE move, several hierarchical sets of xyz axes may be in use at one time. For example, one set may be referred to the screen, another to the picture, a third offset to some point in space (reference axis) and a fourth global axis controlling any number of objects together. See also: DVE, Keyframe
AC-3 See Dolby Digital
Accommodation (Stereoscopic)
The ability of our eyes to refocus at a new point of interest. In normal vision, the processes of focusing on objects at different distances (accommodation) and convergence/divergence (the angle between the lines of sight of our eyes) are linked by muscle reflex. A change in one creates a complementary change in the other. However, watching a stereoscopic film or TV program requires the viewer to break the link between these different processes by accommodating at a fixed distance (the screen) while dynamically varying eye convergence and divergence (something we don't do in life and can quickly lead to headaches if over- used in stereo3D) to view objects at different stereoscopic distances.
Active line The part of a television line that actually includes picture information. This is usually over 80 per cent of the total line time. The remainder of the time was reserved for scans to reset to the start of the next line in camera tubes and CRT screens. Although the imaging and display technologies have moved on to chips and panels, there remains a break (blanking) in the sampling of digital TV as in ITU-R BT.601 and ITU-R BT 709. These 'spaces' carry data for the start of lines and pictures, as well as other information such as embedded audio tracks. See also: Active picture
Active picture The area of a TV frame that carries picture information. Outside the active area there are line and field blanking which roughly, but not exactly, correspond to the areas defined for the original 525- and 625-line analog systems. In digital versions of these, the blanked/active areas are defined by ITU-R BT.601, SMPTE RP125 and EBU-E.
ADC or A/D Analog to Digital Conversion. Also referred to as digitization or quantization. The conversion of analog signals into digital data - normally for subsequent use in digital equipment. 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 8 or 10 bits are normally used; for sound, 16, 20 or 24 bits are common. For pictures the samples are called pixels, which contain data for brightness and color. See also: AES/EBU, Binary, Bit, Into digits (Tutorial 1), Pixel
ADSL Asymmetrical Digital Subscriber Line - working on the copper 'local loop' normally used to connect phones, ADSL provides a broadband downstream channel (to the user) of maximum 8 Mb/s and a narrower band upstream channel (from the user) of maximum 128-1024 kb/s, according to class. Exactly how fast it can run ultimately depends on the performance of the line, often dictated by the distance from the telephone exchange where the DSLAM terminates the line. See also: Broadband, DSL
AES/EBU The Audio Engineering Society (AES) and the EBU (European Broadcasting Union) together have defined a standard for Digital Audio, now adopted by ANSI (American National Standards Institute). Commonly referred to as 'AES/EBU' and officially as AES3, this digital audio standard permits
a variety of sampling frequencies, for example CDs at 44.1 kHz, or DATs and digital VTRs at 48 kHz. 48 kHz is widely used in broadcast TV production although 32-192 kHz are allowed. One cable and connector, usually an XLR, carries two channels of digital audio. See also: Word clock Website: www.aes.org
Aliasing Undesirable 'beating' effects caused by sampling frequencies being too low to faithfully reproduce image detail. Examples are: 1) Temporal aliasing - e.g. wagon wheel spokes apparently reversing, also movement judder seen in the output of standards converters with insufficient temporal filtering. 2) Raster scan aliasing - twinkling effects on sharp boundaries such as horizontal lines. Due to insufficient filtering this vertical aliasing and its horizontal equivalent are often seen in lower quality DVEs as detailed images are compressed. The 'steppiness' or 'jaggies' of poorly filtered lines presented at an angle to the TV raster is also referred to as aliasing. See also: Anti-aliasing, Interpolation (temporal & spatial), Into digits (Tutorial 1)
Aliens A familiar term for alias effects, such as ringing, contouring and jaggy edges caused by lack of resolution in a raster image. Some can be avoided by careful filtering or dynamic rounding.
Alpha channel Another name for key channel - a channel to carry a key signal. See also: Keying, 4:4:4:4
Anaglyph (Stereoscopic) A type of stereoscopy in which the left eye and right eye images are separated by color filtering and then superimposed as a single image rather than two separate images. Each eye sees only the required image through the use of complementary colored filters (e.g. red and green or red and cyan). Anaglyph glasses have been popular over the years for viewing 3D comics and some 3D films (particularly on VHS and DVD). See also: 3D
Anamorphic Generally refers to the use of 16:9 aspect ratio pictures in a 4:3 system. See also: Aspect ratio - of pictures
Answer print The answer print, also called the first trial print, is the first print made from edited film and sound track. It includes fades, dissolves and other effects. It is used as the last check before running off the release prints from the internegatives.
Anti-aliasing Smoothing of aliasing effects by filtering and other techniques. Most, but not all, DVEs and character generators contain anti-aliasing facilities. See also: Aliasing, Interpolation (spatial), Interpolation (temporal)
API Application Programming Interface - a set of interface definitions (functions, subroutines, data structures or class descriptions) which provide a convenient interface to the functions of a subsystem. They also simplify interfacing work by insulating application programmers from minutiae of the implementation.
Arbitrated Loop (AL) A technique used on computer networks to ensure that the network is clear before a fresh message is sent. When it is not carrying data frames, the loop carries 'keep-alive' frames. Any node that wants to transmit places its own ID into a 'keep-alive' frame. When it receives that frame back it knows that the loop is clear and that it can send its message. See also: Fiber Channel
ARC Aspect Ratio Converters change picture aspect ratio - usually between 16:9 and 4:3. Whilst changing the aspect ratio of pictures, the objects within should retain their original shape with the horizontal and vertical axes expanded equally. See also: Aspect ratio
Archive Long-term storage of information. Pictures, sound and metadata stored in digital form can be archived and recovered without loss or distortion. The storage medium must be both reliable and stable and, as large quantities of information need to be stored, cost is of major importance. For archiving stills and graphics any compression should be avoided as full detail is required for viewing their detail. Traditionally, material is archived after its initial use - at the end of the process. More recently some archiving has moved to the beginning. An example is news where, in some cases, new material is archived and subsequent editing etc., accesses this. This reflects the high value of video assets where rapidly increasing numbers of television channels are seeking material. See also: AAF, Data recorders, DTF, Optical disks
Areal density The density of data held on an area of the surface of a recording medium also known as bit density. This is one of the parameters that manufacturers of disk drives and tape recorders strive to increase. It is usually expressed in bits per square inch (PSI). For example some currently available high-capacity drives achieve over 15 Gb/square inch. Capacities and performance can still be expected to continue to grow for some time yet. Much of the latest gain has been made by perpendicular recording that stores data tracks down into the disk, as well as on the surface. See also: Hard disk drives
ARPU Average Revenue Per Unit - usually used by telecoms companies, to describe the money made from each 'unit' or 'customer'.
Artifact Particular visible effects which are a direct result of some technical limitation. Artifacts are generally not described by traditional methods of signal evaluation. For instance, the visual perception of contouring in a picture cannot be described by a signal-to-noise ratio or linearity measurement.
ASCII American Standard Code for Information Interchange. This is a standard computer character set used throughout the industry to represent keyboard characters as digital information.
ASIC Application-Specific Integrated Circuit. Custom-designed integrated circuit with functions specifically tailored to an application. ASICs are only
ATSC The (US) Advanced Television Systems Committee. Established in 1982 to co-ordinate the development of voluntary national technical standards for the generation, distribution and reception of high definition television. In 1995 the ATSC published 'The Digital Television Standard' which describes the US Advanced Television System. See also: VSB, Table 3, Dolby Digital (DD/AC-3), MPEG-2 Website: www.atsc.org
viable for very large-scale high volume products due to high startup costs and their inflexibility. Other programmable devices, such as FPGAs (field programmable gate arrays), offer more flexible and cheaper opportunities for small to medium-sized production levels. See also: PLD
Aspect ratio
1. - of pictures. The ratio of length to height of pictures. All TV screens used to be 4:3, i.e. four units across to three units in height, but now almost all new models, especially where there is digital television, are widescreen,16:9. Pictures presented this way are believed to absorb more of our attention and have obvious advantages in certain productions, such as sport. In the change towards 16:9 some in- between ratios have been used for transmission, such as 14:9. See also: Anamorphic, Widescreen, HDTV
2. - of pixels. The aspect ratio of the area of a picture described by one pixel. The ITU-R BT.601 digital coding standard defines luminance pixels which are not square. In the 525/60 format there are 486 active lines each with 720 samples of which 711 may be viewable due to blanking. Therefore the pixel aspect ratios on 4:3 and 16:9 screens are: 486/711 x 4/3 = 0.911 (tall 487/711 x 16/9 = 1.218 (wide) For the 625/50 format there are 576 active lines each with 720 samples of which 702 are viewable so the pixel aspect ratios are: 576/702 x 4/3 = 1.094 (wide) 576/702 x 16/9 = 1.458 (wider) The digital HD image standards all define square pixels. Account must be taken of pixel aspect ratios when, for example, executing DVE moves such as rotating a circle. The circle must always remain circular and not become elliptical. Another area where pixel aspect ratio is important is in the movement of images between platforms, such as computers and television systems. Computers generally use square pixels so their aspect ratio must be adjusted for SD television-based applications. See also: ARC, Pixel
Asynchronous (data transfer) Carrying no separate timing information. There is no guarantee of time taken but a transfer uses only small resources as these are shared with many others. A transfer is 'stop-go' - depending on handshakes to check data is being received before sending more. Ethernet is asynchronous. Being indeterminate, asynchronous transfers of video files are used between storage devices, such as disks, but are not ideal for 'live' operations. See: Ethernet, Isochronous, Synchronous
ATM Asynchronous Transfer Mode (ATM) provides connections for reliable transfer of streaming data, such as television. With speeds ranging up to 10Gb/s it is mostly used by telcos. 155 and 622Mb/s are most appropriate for television operations. Unlike Ethernet and Fibre Channel, ATM is connection- based: offering good Quality of Service (QoS) by establishing a path through the system before data is sent. Website: www.atmforum.com
ATV Advanced Television. The term used in North America to describe television with capabilities beyond those of analog NTSC. It is generally taken to include digital television (DTV) and high definition (HDTV).
Auditory masking The psycho-acoustic phenomenon of human hearing where what can be heard is affected by the components of the sound. For example, a loud sound will mask a soft sound close to it in frequency. Audio compression systems such as Dolby Digital and MP3 audio use auditory masking as their basis and only code what can be heard by the human ear. See also: Dolby Digital, MP3
AVC See MPEG-4
AVCHD Advanced Video Codec High Definition, a joint development between Panasonic and Sony, applies MPEG-4's AVC video coding and Dolby Digital (AC-3) or linear PCM audio coding, to meet the needs of the high definition consumer market with 1080i and 720p formats. The use of AVC provides at least twice the efficiency of MPEG-2 coding, used in HDV and MiniDV, to offer longer recording times or better pictures - or both. Possible recording media include standard DVD disks, flash memory and hard drives.
AVC-Intra A codec that is H.264-compliant and uses only intra-frame compression. AVC-Intra technology, aimed at professional users, has been adopted by Panasonic for its P2 cameras (AVC-Intra P2) and offers considerably more efficient compression than the original DVCPRO HD codec - maybe as much as 2:1. See also: DVCPRO P2, MPEG-4
AVI (.avi) Audio Video Interleave - a Microsoft multimedia container format introduced in 1992 as part of its Video for Windows technology. AVI files can hold audio and video data in a standard container and provide synchronous video/audio replay. Most AVI files also use the OpenDML file format extensions, forming AVI 2.0 files. Some consider AVI outdated, as there are significant overheads using it with popular MPEG-4 codecs that seemingly unduly increase file sizes. Despite that, it remains popular among file-sharing communities - probably due to its high compatibility with existing video editing and playback software, such as Windows Media Player.