Dubbs :: Technical Glossary

Technical Glossary



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3:2 Pull-Down	« top of page
Method used to map the 24 fps of film onto the 30 fps (60 fields) of 525-line TV, so that one film frame occupies three TV fields, the next two, etc. It means the two fields of every other TV frame come from different film frames making operations such as rotoscoping impossible, and requiring care in editing. Some sophisticated equipment can unravel the 3:2 sequence to allow frame-by-frame treatment and subsequently recompose 3:2. The 3:2 sequence repeats every five TV frames and four film frames, the latter identified as A-D. Only film frame A is fully on a TV frame and so exists at one time code only, making it the editable point of the video sequence.
4:1:1
This is a set of sampling frequencies in the ratio 4:1:1, used to digitise the luminance and colour difference components (Y, R-Y, B-Y) of a video signal. The four represents 13.5 MHz, the sampling frequency of Y, and the ones each 3.75 MHz for R-Y and BY With the colour information sampled at half the rate of the 4:2:2 system, this is generally used as a more economical form of sampling for 525-line picture formats. Both luminance and colour difference are still sampled on every line. But the latter has half the horizontal resolution of 4:2:2, while the vertical resolution of the colour information is maintained. For 525-line pictures, this means the colour is fairly equally resolved in horizontal and vertical directions.
4:2:0
A sampling system used to digitise the luminance and colour difference components (Y, R-Y, BY) of a video signal. The four represents the 13.5 MHz sampling frequency of Y, while the R-Y and BY are sampled at 6.75 MHz - effectively between every other line only (one line is sampled at 4:0:0, luminance only, and the next at 4:2:2). This is generally used as a more economical system than 4:2:2 sampling for 625-line formats so that the colour signals have a reasonably even resolution in the vertical and horizontal directions for that format.
4:2:2
A commonly used term for a component digital video format. A ratio of sampling frequencies used to digitise the luminance and colour difference components (Y, R-Y, BY) of a video signal. It is generally used as shorthand for ITU-R 601. The term 4:2:2 describes that for every four samples of Y, there are two samples each of R-Y and BY, giving more chrominance bandwidth in relation to luminance compared to 4:1:1 sampling. ITU-R 601, 4:2:2 is the standard for digital studio equipment and the terms "4:2:2" and "601" are commonly (but technically incorrectly) used synonymously. The sampling frequency of Y is 13.5 MHz and that of R-Y and BY is each 6.75 MHz providing a maximum colour bandwidth of 3.37 MHz-enough for high-quality chromakeying. The format specifies eight bits of resolution.
4:2:2:4
Same as 4:2:2, but with the addition of a key channel that is sampled four times for every four samples of the luminance channel.
4:4:4
Similar to 4:2:2, except that for every four luminance samples, the colour channels are also sampled four times.
4:4:4:4
Similar to 4:2:2:4, except that for every four luminance samples, the colour and key channels are also sampled four times.

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ADC (A-D, A/D, A-to-D) Analogue to Digital Conversion	« top of page
Also referred to as digitisation or quantisation The conversion of an analogue 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 analogue amplitude information - how many bits are used to describe the analogue 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 colour See also: Binary, Bit.
AES/EBU
Informal name for a digital audio standard established jointly by the AES (Audio Engineering Society) and EBU (European Broadcasting Union) organisations. The sampling frequencies for this standard vary depending on the format being used; the sampling frequency for D1 and D2 audio tracks is 48 kHz.
AIF - Audio Interchange File
An audio file format developed by Apple Computer to store high quality sampled sound and musical instrument information. The AIF files are a popular format for transferring between the Macintosh and the PC. see also WAV
Algorithm
A formula or set of steps used to simplify, modify, or predict data. Complex algorithms are used to selectively reduce the high digital audio and video data rates. These algorithms utilise physiologists' knowledge of hearing and eyesight. For example, we can resolve fine detail in a still scene, but our eye cannot resolve the same detail in a moving scene. Using knowledge of these limitations, algorithms are formulated to selectively reduce the data rate without affecting the viewing experience. see also compression, MPEG, JPEG
Aliasing
Defects or distortion in a television picture. In analogue video, aliasing is typically caused by interference between two frequencies such as the luminance and chrominance frequencies or the chrominance and field scanning frequencies. It appears as moiré or herringbone patterns, straight lines that become wavy, or rainbow colours. In digital video, aliasing is caused by insufficient sampling or poor filtering of the digital video. Defects are typically seen as jagged edges on diagonal lines and twinkling or brightening (beating) in picture detail.
Analogue
is a term used to describe something that is analogous (representative) of something - in the case of television this is a video or audio signal. An analogue recording on tape can be displayed on an oscilloscope and is seen as a complex mixture of constantly changing wavy lines - the lines show all the different aspects of the signal. Simplistically the peaks and troughs of the lines represent amplitude (volume in audio - luminance [brightness] in video) - the distance from one peak (or trough) to the next represents frequency. An easy, everyday example of an analogue 'recording' would be a photocopy - the copy is analogous, but not identical, to the original, the image is always slightly degraded. If the photocopy is then copied and this copy is copied - the quality of the image gets worse and worse. The same applies to analogue video and audio recordings. Obviously development of recording techniques have meant that this degradation is kept to a minimum and often the degrading of the copy can only be detected after it is several generations removed from the original or if the quality of the recording format is inferior. (I.e. a second generation VHS copy will look far worse than a second generation Betacam SP copy). see also digital
Artifacts
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 analogue are cross colour and cross luminance. Most common in digital are macroblocks, which resemble pixelation of the video image.
Aspect ratio
The ratio of television picture width to height. In NTSC and PAL video, the present standard is 4:3. In widescreen video, it is typically 16:9, however, 14:9 has been used as a transition.
AVI - Audio Video Interleaving
The Microsoft Video for Windows file format for combining video and audio into a single block in time such as a 1/30th second video frame. In this file format, blocks of audio data are woven into a stream of video frames. ASF is intended to supersede AVI.

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Bandwidth	« top of page
1. The complete range of frequencies over which a circuit or electronic system can function with minimal signal loss, typically less than 3 dB. 2. The information-carrying capability of a particular television channel. In PAL systems, the bandwidth limits the maximum visible frequency to 5.5 MHz, in NTSC, 4.2 MHz. The ITU-R 601 luminance channel sampling frequency of 13.5 MHz was chosen to permit faithful digital representation of the PAL and NTSC luminance bandwidths without aliasing. In transmission, the United States analogue and digital television channel bandwidth is 6 MHz.
Bel
A measure of voltage, current, or power gain. One bel is defined as a tenfold increase in power. If an amplifier increases a signal's power by 10 times, its power gain is 1 bel or 10 decibels (dB). If power is increased by 100 times, the power gain is 2 bels or 20 decibels. 3 dB is considered a doubling.
Betacam
An analogue component VTR system using a 1/2-inch tape cassettes. This was developed by Sony and is marketed by them and several other manufacturers. Although recording the Y, R-Y and BY component signals onto tape many machines are operated with coded (PAL or NTSC) video in and out. The system has continued to be developed over the years to offer models for the industrial and professional markets as well as full luminance bandwidth (Betacam SP), PCM audio and SDI connections. Digital versions exist as the high-end Digital Betacam and Betacam SX for ENG and similar applications.
Betacam SX & other Digital Formats
see the Digital Formats Chart
Binary
A numbering system in base-2, only using the digits 0 and 1. In computer systems, the binary digits are represented by two different voltages or currents, one corresponding to 0 and the other corresponding to 1. All computer programs are executed in binary form. Binary representation requires a greater number of digits than the base 10 decimal system more commonly used. For example, the base 10 number 254 is 11111110 in binary. The result of a binary multiplication contains the sum of digits of the original numbers. So: 10101111 x 11010100 = 1001000011101100 (In decimal 175 x 212 = 37,100) (From right to left, the digits represent 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 16384, 32768) Each digit is known as a bit. This example multiplies two 8-bit numbers to produce a 16-bit result - a very common process in digital television equipment. see also bit, byte
Bit
Binary digit. The smallest unit of data in a digital system. A bit is a single one or zero. A group of bits, such as 8-bits or 16-bits, compose a byte. The number of bits in a byte depends upon the processing system being used. Typical byte sizes are 8, 16, and 32. see also binary, byte
Bitmap
2-D array of pixels representing video and graphics.
Bit stream
A continuous series of bits transmitted on a line.
Broadband
1. A response that is the same over a wide range of frequencies. 2. Capable of handling frequencies greater than those required for high-grade voice communications (higher than 3 to 4 kilohertz).
Broadcast FTP Protocol (BFTP)
A one-way IP multicast based resource transfer protocol, the unidirectional Broadcast File Transfer Protocol (BFTP) is a simple, robust, one-way resource transfer protocol that is designed to efficiently deliver data in a one-way broadcast-only environment. This transfer protocol is appropriate for IP multicast over television vertical blanking interval (IPVBI), in IP multicast carried in MPEG-2, like with the DVB multiprotocol encapsulation, or in other unidirectional transport systems. It delivers constant bitrate (CBR) services or opportunistic services, depending on the characteristics and features of the transport stream multiplexor or VBI insertion device.
Byte
A group of data bits that are processed together. Typically, a byte consists of 8, 16, 24 or 32 bits. 1 Byte = 8 bits = 256 discrete values (brightness, colour, etc.) 1 kilobyte = 210 bytes = 1,024 bytes: (not 1000 bytes) 1 Megabyte = 220 bytes = 1,048,576 bytes: (not 1 million bytes) 1 Gigabyte = 230 bytes = 1,073,741,824 bytes: (not one billion bytes) 1 Terabyte = 240 bytes = 1,099,511,627,776 bytes: (not one trillion bytes) A full frame of digital television, sampled according to ITU-R 601, requires just under 1 Mbyte of storage (701 Kbytes for 525 lines, 829 Kbytes for 625 lines). HDTV frames are 4-to-5 times as large and digital film frames may be that much larger again. see also binary, bit

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Chromakeying	« top of page
The process of overlaying one video signal over another, the areas of overlay being defined by a specific range of colour, or chrominance, on the foreground signal. For this to work reliably, the chrominance must have sufficient resolution, or bandwidth. PAL or NTSC coding systems restrict chroma bandwidth and so are of very limited use for making a chromakey which, for many years, was restricted to using live, RGB camera feeds. An objective of the ITU-R 601 digital sampling standard was to allow high quality chromakeying in post production. The 4:2:2 sampling system allowed far greater bandwidth for chroma than PAL or NTSC and helped chromakeying, and the whole business of layering, to thrive in post production. High signal quality is still important and anything but very mild compression tends to result in keying errors appearing - especially at DCT block boundaries. Chromakeying techniques have continued to advance and use many refinements, to the point where totally convincing composites can be easily created. You can no longer "see the join" and it may no longer be possible to distinguish between what is real and what is keyed.
Chrominance
The colour component of a video signal that includes information about hue and saturation. See also luminance
Cinepak
A high-quality medium bandwidth compression that is not real-time but can play back in software. Its 24-bit format produces high-quality video at 320 x 240 resolution and 15 frames per second at a 150 Kbps data rate. Commonly a CD-ROM solution developed a number of years ago and not a competitor to more modern techniques.
Clone
An exact copy, indistinguishable from the original. As in copying recorded material, for example a copy of a non-compressed recording to another non-compressed recording. If attempting to clone compressed material care must be taken not to decompress it as part of the process or the result will not be a clone.
Codec (coder-decoder)
A device that converts analogue video and audio signals into a digital format for transmission over telecommunications facilities and also converts received digital signals back into analogue format.
Coding
Representing each video signal level as a number, usually in binary form.
Component & Composite
Component and Composite are terms used to describe a video signal. A component signal consists of the luminance (Y) and chrominance [brightness and colour] information separated (Y, Red-Y, Blue-Y) . The signal is separated into three and would be passed down three separate wires. The component signal applies to both analogue and digital video. A composite signal combines both the luminance and chrominance information together with colour coding information (either PAL, NTSC or SECAM). The composite signal would pass down one wire. To summarise, the best possible digital system is component, and the best possible analogue system is also component. Component is either 625 or 525 lines. Composite can be 625 PAL, 625 SECAM or 525 NTSC (it could even be 525 PAL as in Brazil!).
Component Digital Post Production
A method of post production that records and processes video completely in the component digital domain. Analogue sources are converted only once to the component digital format and then remain in that format throughout the post production process.
Compression
Reduction of the size of digital data files by removing redundant information (loss-less) or removing non-critical data (lossy). Pictures are analysed looking for redundancy and repetition and so discard unnecessary data. The techniques were primarily developed for digital transmission but have been adopted as a means of handling digital video in computers and reducing the storage demands for digital VTRs. Compression can be at either a set rate or a variable rate. Also known as Bit Rate Reduction (BRR) see also algorithm, compression, MPEG
Compression Artifacts
Compacting of a digital signal, particularly when a high compression ratio is used, may result in small errors when the signal is decompressed. These errors are known as "artifacts," or unwanted defects. The artifacts may resemble noise (or edge "busyness") or may cause parts of the picture, particularly fast moving portions, to be displayed with the movement distorted or missing.
Compression Ratio
The ratio of the data in the non-compressed digital video signal to the compressed version. Modern compression techniques start with the ITU-R 601 component digital television signal so the amount of data of the non-compressed video is well defined - 76 GBytes/hour for the 525/60 standard and 75 GBytes/hour for 625/50. The compression ratio should not be used as the only method to assess the quality of a compressed signal. For a given technique greater compression can be expected to result in worse quality but different techniques give widely differing quality of results for the same compression ratio. The only sure method of judgement is to make a very close inspection of the resulting pictures.

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D1, D2, etc & other Digital Formats	« top of page
see the Digital Formats Chart
DA-88
A Tascam-brand eight track digital audio tape machine using the 8 mm video format of Sony. It has become the de facto standard for audio post production though there are numerous other formats, ranging from swappable hard drives to analogue tape formats and everything in between. see also Digital Tape Formats
Data Compression
A technique that provides for the transmission or storage, without noticeable information loss, of fewer data bits than were originally used when the data was created.
DBS - Digital Broadcast System
An alternative to cable and analogue satellite reception initially utilising a fixed 18-inch dish focused on one or more geostationary satellites. DBS units are able to receive multiple channels of multiplexed video and audio signals as well as programming information, Email, and related data. DBS typically uses MPEG-2 encoding and COFDM transmission. Also known as digital satellite system.
DCT - Discrete Cosine Transform.
1. A widely used method of data compression of digital video pictures basically by resolving blocks of the picture (usually 8 x 8 pixels) into frequencies, amplitudes, and colours. JPEG and DV depend on DCT. 2. Also an Ampex data videotape format using discrete cosine transform.
Digital
is the generic term used for the processing, recording etc of information (data) using binary code - digits 1 and 0 - which are represented in a recording as two different voltage levels. This makes recording the data relatively simple - the difficult part is sampling the data in the first place! A digital recording can be displayed on a screen, but would mean little, as it would just be a load of binary code. The simple way of looking at the recording is to convert it back to an analogue signal and view it as analogue. Contrary to what we are led to believe you can't view or hear digital images or sound - television tubes and speakers are analogue devices, so the best images and sounds can be spoilt by poor quality analogue technology! To illustrate how digital recording works is not easy, but a photocopy test can be done! If a code is written on a piece of paper and copied then the copy copied etc - the quality of the image gets worse and worse, but the code can still be read, this is the real advantage of digital processing, as long as the code is in tact it will represent an exact copy of the original. This is why a digital copy is referred to as a 'clone' - an exact replica of the original. see also analogue
Digital Betacam (DigiBeta)
see the Digital Formats Chart
Dolby Digital (formerly Dolby AC-3)
The approved 5.1 channel (surround-sound) audio standard for ATSC digital television, using approximately 13:1 compression Six discrete audio channels are used: Left, Centre, Right, Left Rear (or side) Surround, Right Rear (or side) Surround, and a subwoofer (considered the ".1" as it is limited in bandwidth). The bit rate can range from 56 kbps to 640 kbps, typically 64 kbps mono, 192 kbps two-channel, 320 kbps 35mm Cinema 5.1, 384 kbps Laserdisc/DVD 5.1 and ATSC, 448 kbps 5.1. When moving from analogue recording to a digital recording medium, the digital audio coding used yields an amount of data often too immense to store or transmit economically, especially when multiple channels are required. As a result, new forms of digital audio coding - often known as "perceptual coding" - have been developed to allow the use of lower data rates with a minimum of perceived degradation of sound quality. Dolby's third generation audio coding algorithm (originally called AC-3) is such a coder. This coder has been designed to take maximum advantage of human auditory masking in that it divides the audio spectrum of each channel into narrow frequency bands of different sizes, optimised with respect to the frequency selectivity of human hearing. This makes it possible to sharply filter coding noise so that it is forced to stay very close in frequency to the frequency components of the audio signal being coded. By reducing or eliminating coding noise wherever there are no audio signals to mask it, the sound quality of the original signal can be subjectively preserved. In this key respect, a coding system like Dolby Digital is essentially a form of very selective and powerful noise reduction.
Dolby E
A new coding system designed specifically for use with video available from Dolby Laboratories. The audio framing is matched to the video framing, which allows synchronous and seamless switching or editing of audio and video without the introduction of gaps or A/V sync slips. All of the common video frame rates, including 30/29.97, 25, and 24/23.976, can be supported with matched Dolby E audio frame sizes. The Dolby E coding technology is intended to provide approximately 4:1 reduction in bit rate. The reduction ratio is intentionally limited so that the quality of the audio may be kept very high even after a number of encode-decode generations. The fact that operations such as editing and switching can be performed seamlessly in the coded domain allows many coding generations to be avoided, further increasing quality. A primary carrier for the Dolby E data will be the AES/EBU signal. The Dolby E coding will allow the two PCM audio channels to be replaced with eight encoded audio channels. A VTR PCM track pair will become capable of carrying eight independent audio channels, plus the accompanying metadata. The system is also intended to be applied on servers and satellite links. A time delay when encoding or decoding Dolby E is unavoidable. In order to facilitate the provision of a compensating video delay, the audio encoding and decoding delay have been fixed at exactly one frame. When applied with video recording formats which incorporate frame based video encoding, it can be relatively easy to provide for equal video and audio coding delays. When applied with uncoded video, it may be necessary to provide a compensating one frame video delay.
Dolby Surround (Dolby Stereo, & Dolby 4:2:4)
Matrix Analogue coding of four audio channels - Left, Centre, Right, Surround (LCRS), into two channels referred to as Right-total and Left-total (Rt, Lt). On playback, a Dolby Surround Pro Logic decoder converts the two channels to LCRS and, optionally, a subwoofer channel. The Pro Logic circuits are used to steer the audio and increase channel separation. The Dolby Surround system, originally developed for the cinema, is a method of getting more audio channels but suffers from poor channel separation, a mono limited bandwidth surround channel and other limitations. A Dolby Surround track can be carried by analogue audio or linear PCM, Dolby Digital and MPEG compression systems.
DV
This digital VCR format is a co-operation between Hitachi, JVC, Sony, Matsushita, Mitsubishi, Philips, Sanyo, Sharp, Thomson and Toshiba. It uses 6.35 mm (0.25-inch) wide tape in a range of products to record 525/60 or 625/50 video for the consumer (DV) and professional markets (Panasonic's DVCPRO, Sony's DVCAM and Digital-8). All models use digital intra-field DCT-based "DV" compression (about 5:1) to record 8-bit component digital video based on 13.5 MHz luminance sampling. The consumer versions, DVCAM, and Digital-8 sample video at 4:1:1 (525/60) or 4:2:0 (625/50) video (DVCPRO is 4:1:1 in both 525/60 and 625/25) and provide two 16-bit/48 or 44.1 kHz, or four 12-bit/32 kHz audio channels onto a 4 hour 30 minutes standard cassette or smaller 1 hour "mini" cassette. The video recording rate is 25 Mbps.
DVD - Digital Versatile Disk
A high density development of the compact disk. It is the same size as a CD but stores from 4.38 GB (seven times CD capacity) on a single sided, single layer disk. DVDs can also be double sided or dual layer-storing even more data. The capacities commonly available at present: DVD-5: 4.7 GB (1 side, 1 layer) DVD-9: 8.5 GB (1 side, 2 layers) DVD-10: 9.4 GB (2 sides, 1 layer each) DVD-18: 17.0 GB (2 sides, 2 layers) DVD-R: 4.7 GB (1 side, 1 layer) (write once) DVD-RAM: 2.6 GB (per side, 1 layer) (rewritable) DVD-RAM: 4.7 GB (per side, 1 layer) (rewritable)

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EBU - European Broadcasting Union	« top of page
An organisation of European broadcasters that, among other activities, produces technical statements and recommendations for the 625/50 line television system. CP 67, CH-1218 Grand-Saconnex GE, Switzerland. Tel: 011-41-22-717-2221. Fax: 011-41-22-717-2481. Email: ebu@ebu.ch Internet: www.ebu.ch
Embedded audio
Digital audio that is multiplexed and carried within an SDI connection - so simplifying cabling and routing. The standard (ANSI/SMPTE 272M-1994) allows up to four groups each of four mono audio channels. Generally VTRs only support Group 1 but other equipment may use more, for example Quantel's Clipbox server connection to an edit seat uses groups 1-3 (12 channels). 48 kHz synchronous audio sampling is pretty well universal in TV but the standard also includes 44.1 and 32 kHz synchronous and asynchronous sampling. Synchronous means that the audio sampling clock is genlocked to the associated video (8,008 samples per five frames in 525/60, 1,920 samples per frame in 625/50). Up to 24-bit samples are allowed but mostly only up to 20 are currently used. 48 kHz sampling means an average of just over three samples per line, so three samples per channel are sent on most lines and four occasionally - the pattern is not specified in the standard. Four channels are packed into an Ancillary Data Packet and sent once per line (hence a total of 4 x 3 = 12 or 4 x 4 = 16 audio samples per packet per line).
Encryption
The process of coding data so that a specific code or key is required to restore the original data. In broadcast, this is used to make transmissions secure from unauthorised reception as is often found on satellite or cable systems.
Error concealment
In digital video recording systems, a technique used when error correction fails. Erroneous data is replaced by data synthesised from surrounding pixels.
Error correction
In digital video recording systems, a scheme that adds overhead to the data to permit a certain level of errors to be detected and corrected.
Error detection
Checking for errors in data transmission. A calculation is made on the data being sent and the results are sent along with it. The receiver then performs the same calculation and compares its results with those sent. If an error is detected the affected data can be deleted and retransmitted, the error can be corrected or concealed, or it can simply be reported.

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Fibre optics	« top of page
Thin glass filaments within a jacket that optically transmits images or signals in the form of light around corners and over distances with extremely low losses.
Field
In an interlaced-scanning format, a frame consists of a field of even scan lines or a field of odd scan lines captured or displayed at different times. In a progressive-scanning format, a field is the same as a frame. See also: Frame
FireWire
Apple Computer's trademark for IEEE 1394. see also IEEE 1394
Frame
A frame is one complete image in a sequence of images. In video, the frame captures and displays all pixels and lines of an image. In a progressive-scanning format, there is no decomposition into fields. In an interlaced-scanning format, the frame consists of odd and even line fields, captured or displayed at different times, which in combination contain all pixels and lines of an image. The frame rate of a progressive scan format is twice that of an interlace scan format.
Frame buffer
Memory used to store a complete frame of video.
Freeze frame
The storing of a single frame of video.

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Generation (loss)	« top of page
The signal degradation caused by successive recordings. Freshly recorded material is first generation, one re-recording, or copy, makes the second, etc. This is of major concern in analogue linear editing but much less so using a digital suite. Non-compressed component DVTRs should provide at least twenty generations before any artifacts become noticeable, but the very best multi-generation results are possible with disk-based systems. Generations are effectively limitless. Besides the limitations of recording, the action of processors such as decoders and coders will make a significant contribution to generation loss. The decode/recode cycle of NTSC and PAL is well known for its limitations but equal caution is needed for digital video compression systems, especially those using MPEG, and the colour space conversions that typically occur between computers handling RGB and video equipment using Y, Cr, Cb. see also: error concealment, error correction, error detection.
GIF - Graphics Interchange Format
A computer graphics file format developed by CompuServe for use in compressing graphic images, now commonly used on the Internet. GIF compression is lossless, supports transparency, but allows a maximum of only 256 colours. Images that will gain the most from GIF compression are those which have large areas (especially horizontal area) with no changes in colour.

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HD D5	« top of page
A compressed recording system developed by Panasonic which uses compression at about 4:1 to record HD material on standard D5 cassettes. HD D5 supports the 1080 and the 1035 interlaced line standards at both 60 Hz and 59.94 Hz field rates, all 720 progressive line standards and the 1080 progressive line standard at 24, 25 and 30 frame rates. Four uncompressed audio channels sampled at 40 kHz, 20 bits per sample, are also supported.
HDCAM
Sometimes called HD Betacam - is a means of recording compressed high-definition video on a tape format (1/2-inch) which uses the same cassette shell as Digital Betacam, although with a different tape formulation. The technology is aimed specifically at the USA and Japanese 1125/60 markets and supports both 1080 and 1035 active line standards. Quantisation from 10 bits to 8 bits and DCT intra-frame compression are used to reduce the data rate. Four uncompressed audio channels sampled at 48 kHz, 20 bits per sample, are also supported.
HDTV - High Definition Television
The 1,125-, 1,080- and 1,035-line interlace and 720 and 1,080-line progressive formats in a 16:9 aspect ratio. Officially a format is high definition if it has at least twice the horizontal and vertical resolution of the standard signal being used. There is a debate as to whether 480-line progressive is also high definition. It is the opinion of the editors that 480-line progressive is not an HDTV format, but does provide better resolution than 480-line interlace, making it an enhanced definition format.

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IEEE 1394 (FireWire)	« top of page
A low-cost digital interface originated by Apple Computer as a desktop LAN and developed by the IEEE 1394 working group. Can transport data at 100, 200, or 400 Mbps. One of the solutions to connect digital television devices together at 200 Mbps. Serial Bus Management provides overall configuration control of the serial bus in the form of optimising arbitration timing, guarantee of adequate electrical power for all devices on the bus, assignment of which IEEE 1394 device is the cycle master, assignment of isochronous channel ID, and notification of errors. There are two types of IEEE 1394 data transfer: asynchronous and isochronous. Asynchronous transport is the traditional computer memory-mapped, load and store interface. Data requests are sent to a specific address and an acknowledgement is returned. In addition to an architecture that scales with silicon technology, IEEE 1394 features a unique isochronous data channel interface. Isochronous data channels provide guaranteed data transport at a pre-determined rate. This is especially important for time-critical multimedia data where just-in-time delivery eliminates the need for costly buffering. see also FireWire
Illegal colours
Colours that force a colour system to go outside its normal bounds. Usually these are the result of electronically painted images rather than direct camera outputs. For example, removing the luminance from a high intensity blue or adding luminance to a strong yellow in a paint system may well send a subsequent NTSC or PAL coded signal too high or low - producing at least inferior results and maybe causing technical problems. Out of gamut detectors can be used to warn of possible problems.
IMX & other Digital Formats
Please see the Digital Formats Chart
Interlaced
Short for interlaced scanning. Also called line interlace. A system of video scanning whereby the odd- and even-numbered lines of a picture are transmitted consecutively as two separate interleaved fields. Interlace is a form of compression.
Interpolation (spatial)
When re-positioning or re-sizing a digital image inevitably more, less or different pixels are required from those in the original image. Simply replicating or removing pixels causes unwanted artifacts. For far better results the new pixels have to be interpolated - calculated by making suitably weighted averages of adjacent pixels - to produce a more transparent result. The quality of the results will depend on the techniques used and the number of pixels (points - hence 16-point interpolation), or area of original picture, used to calculate the result.
Interpolation (temporal)
Interpolation between the same point in space on successive frames. It can be used to provide motion smoothing and is extensively used in standards converters to reduce the judder caused by the 50/60 Hz field rate difference. The technique can also be adapted to create frame averaging for special effects.
ISDN - Integrated services digital network
Allows data to be transmitted at high speed over the public telephone network. ISDN operates from the Basic Rate of 64 kbits/sec to the Primary Rate of 2 Mbps (usually called ISDN-30 as it comprises 30 Basic Rate channels). Most of the Western world currently has the capability to install ISDN-2 with 128 kbps and very rapid growth is predicted for ISDN generally. In the television and film industries, audio facilities are already using it. The cost of a call is usually similar to using a normal telephone. Nominally ISDN operates internationally, but there are variations in standards, service and ISDN adapter technologies. Some operators in the USA use a similar system, Switch 56 (56 kbits/sec and upwards), although the availability of ISDN is becoming wider.

j
Java	« top of page
A general purpose programming language developed by Sun Microsystems and best known for its widespread use on the World Wide Web. Unlike other software, programs written in Java can run on any platform type (including set-top boxes), as long as they contain a Java Virtual Machine. Internet: java.sun.com.
JPEG - Joint Photographic Experts Group
ISO/ITU-T. JPEG is a standard for the data compression of still pictures (intrafield). In particular its work has been involved with pictures coded to the ITU-R 601 standard. JPEG uses DCT and offers data compression of between two and 100 times and three levels of processing are defined: the baseline, extended and "lossless" encoding. see also compression, MPEG, algorithm

k
Keyframe	« top of page
A set of parameters defining a point in a transition, such as a DVE effect. For example, a keyframe may define a picture size, position and rotation. Any digital effect must have a minimum of two keyframes, start and finish, although more complex moves will use more - maybe as many as 100. Increasingly, more parameters are becoming "keyframeable," meaning they can be programmed to transition between two, or more, states. Examples are colour correction to made a steady change of colour, and keyer settings, perhaps to made an object slowly appear or disappear.

l
Letterbox	« top of page
Image of a widescreen picture on a standard 4:3 aspect ratio television screen, typically with black bars above and below. Used to maintain the original aspect ratio of the source material. see also pillarbox
Live-streaming
Streaming media that is broadcast to many people at a set time.
Lossless compression
Reducing the bandwidth required for transmission of a given data rate without loss of any data.
Lossy compression
Reducing the total data rate by discarding data that is not critical. Both the video and audio for DTV transmission will use lossy compression. see also algorithm
Luminance
The component of a video signal that includes information about its brightness. see also chrominance

m
Megabyte (Mbyte)	« top of page
One million bytes (actually 1,048,576); one thousand kilobytes.
Metadata (side information)
Informational data about the data itself. Typically information about the audio and video data included in the signal's data stream.
Mini DV & other Digital Formats
Please see the Digital Formats Chart
Motion compensation
The use of motion vectors to improve the efficiency of the prediction of pixel values. The prediction uses motion vectors to provide offsets into past and/or future reference frames containing previously decoded pixels that are used to form the prediction and the error difference signal.
Motion estimation
An image compression technique that achieves compression by describing only the motion differences between adjacent frames, thus eliminating the need to convey redundant static picture information from frame to frame. Used in the MPEG standards.
Motion-JPEG
Using JPEG compressed images as individual frames for motion. For example, 30 Motion-JPEG frames viewed in one second will approximate 30-frame per second video.
MOV
The file extension used by MooV format video files on Windows. These MOV files are generated with Apple Computer's QuickTime and played on Windows systems via QuickTime for Windows.
MPEG
Compression standards for moving images conceived by the Motion Pictures Expert Group, an international group of industry experts set up to standardise compressed moving pictures and audio. MPEG-2 is the basis for ATSC digital television transmission. Its work follows on from that of JPEG to add interfield compression, the extra compression potentially available through similarities between successive frames of moving pictures. Four MPEG standards were originally planned, but the accommodation of HDTV within MPEG-2 has meant that MPEG-3 is now redundant. MPEG-4 is intended for unrelated applications, however, can be used to display ATSC formats on a PC. The main interest for the television industry is in MPEG-1 and MPEG-2. A group of picture blocks, usually four, which are analysed during MPEG coding to give an estimate of the movement between frames. This generates the motion vectors that are then used to place the macroblocks in decoded pictures. see also compression, JPEG, algorithm
MPEG-1
A group of picture blocks, usually four, which are analysed during MPEG coding to give an estimate of the movement between frames. This generates the motion vectors that are then used to place the macroblocks in decoded pictures. This was designed to work at 1.2 Mbps, the data rate of CD-ROM, so that video could be played from CDs. However the quality is not sufficient for TV broadcast.
MPEG-2
This has been designed to cover a wide range of requirements from "VHS quality" all the way to HDTV through a series of algorithm "profiles" and image resolution "levels." With data rates of between 1.2 and 15 Mbps, there is intense interest in the use of MPEG-2 for the digital transmission of television - including HDTV - applications for which the system was conceived. Coding the video is very complex, especially as it is required to keep the decoding at the reception end as simple and inexpensive as possible. MPEG-2 is the compression used by the ATSC and DVB standards. MPEG can offer better quality pictures at high compression ratios than pure JPEG compression, but with the complexity of decoding and especially coding and the 12-long group of pictures (GoP), it is not an ideal compression system for editing. If any P or B frames are used then even a cut will require the re-use of complex, and not perfect, MPEG coding. However, MPEG Splicers are beginning to appear to alleviate this difficulty. Of the six profiles and four levels creating a grid of 24 possible combinations, 12 have already been implemented. The variations these define are so wide that it would not be practical to build a universal coder or decoder. Interest is now focused on the Main profile, Main level, sometimes written as MP@ML, which covers broadcast television formats up to 720 pixels x 576 lines at 30 frames per second. These figures are quoted as maximums so 720 x 486 at 30 frames are included, as are 720 x 576 at 25 frames. As the coding is intended for transmission the economy of 4:2:0 sampling is used. A recent addition to MPEG-2 is the studio profile. Designed for studio work its sampling is 4:2:2. The studio profile is written as 422P@ML. To improve the picture quality, higher bit rates are used. The first applications for this appear to be in electronic news gathering (ENG), and with some video servers. see also compression, JPEG
MPEG-4
The third standard developed by MPEG. Started in July 1993 MPEG-4 has benefited from the huge R&D investments made by participating companies and provides a harmonised range of responses to the diverse needs of the digital audio-visual industry, including compatibility with other major standards such as H.263 and VRML.
MPEG 4:2:2
Also referred to as Studio MPEG, Professional MPEG and 442P@ML. Sony's Betacam SX is based on MPEG 4:2:2. See: MPEG-2.
MPEG-7
A standardised description of various types of multimedia information. This description will be associated with the content itself, to allow fast and efficient searching for material that is of interest to the user. MPEG-7 is formally called "Multimedia Content Description Interface." The standard does not comprise the (automatic) extraction of descriptions/features. Nor does it specify the search engine (or any other program) that can make use of the description. It is not a new compression standard, but an attempt to manage motion imaging and multimedia technology.
MPEG-21
The Motion Picture Experts Group's attempt to get a handle on the overall topic of content delivery. By defining a Multimedia Framework from the viewpoint of the consumer, they hope to understand how various components relate to each other and where gaps in the infrastructure might benefit from new standards. A technical report on the MPEG-21 framework is scheduled for mid-2000.
MPEG IMX
Sony's trademark for a family of devices, such as DVTRs, that are I frame-only 50 Mbps MPEG-2 streams using Betacam style cassettes. Plays Digital Betacam, Betacam SX, Betacam SP, Betacam, and, MPEG IMX, outputting 50 Mbps MPEG I-frame on SDTI-CP regardless of the tape being played. It can also handle other (lower) input and output data rates, but the recordings are 50 Mbps I-frame in any case.

n
NTSC - National Television System Committee	« top of page
The NTSC is the organisation that developed the analogue television standard currently in use in the USA, Canada, and Japan. The NTSC standard combines blue, red and green signals modulated as an AM signal with an FM signal for audio. The picture is made up of 525 lines with 30 frames (60 fields) per second. The 525 line, 60 field sequence is always linked to a 60 Hz mains frequency. See also PAL & SECAM
Nonlinear
A term used for editing and the storage of audio, video and data. Information (footage) is available anywhere on the media (computer disk or laser disc) almost immediately without having to locate the desired information in a time linear format.
Nonlinear editing
Nonlinear distinguishes editing operation from the "linear" methods used with tape. Nonlinear refers to not having to edit material in the sequence of the final program and does not involve copying to make edits. It allows any part of the edit to be accessed and modified without having to re-edit or re-copy the material that is already edited and follows that point. Nonlinear editing is also non-destructive - the video is not changed but the list of how that video is played back is modified during editing.

o
Off-line (editing)	« top of page
A decision-making process using low-cost equipment usually to produce an EDL or a rough cut which can then be conformed or referred to in a high quality on-line suite - so reducing decision-making time in the more expensive on-line environment. While most off-line suites enable shot selection and the defining of transitions such as cuts and dissolves, very few allow settings for the DVEs, colour correctors, keyers and layering that are increasingly a part of the on-line editing process.

p
PAL - Phase Alternate Line	« top of page
The television broadcast standard throughout Europe (except in France and Eastern Europe, which use SECAM). This standard broadcasts 625 lines of resolution, nearly 20% more than the US standard, NTSC, of 525. There are 25 frames (50 fields) per second making up the picture. The 625 line, 50 field sequence is always linked to a 50 Hz mains frequency. See also NTSC & SECAM
PCM - Pulse Code Modulation
A method by which sound is digitally recorded and reproduced. Sounds are reproduced by modulating (changing) the playback rate and amplitude of the sampled (stored) digital pulses (waves). This enables the PCM sound to be reproduced with a varying pitch and amplitude.
Pillarbox
Describes a frame that the image fails to fill horizontally (a 4:3 image on a 16:9 screen), in the same way that a letterbox describes a frame that the image fails to fill vertically (a 16:9 image on a 4:3 screen) see also letterbox
Pixel
A shortened version of "Picture cell" or "Picture element." The name given to one sample of picture information. Pixel can refer to an individual sample of R, G, B luminance or chrominance, or sometimes to a collection of such samples if they are co-sited and together produce one picture element.
Protocol
Set of syntax rules defining exchange of data including items such as timing, format, sequencing, error checking, etc.

q
QuickTime	« top of page
Apple Computer's system-level software architecture supporting time-based media, giving a seamless integration of video, sound, and animation. For Macintosh and Windows computers.

r
RealAudio	« top of page
Popular software for streaming audio and video over the Internet. made by RealNetworks of Seattle, Washington.
RealVideo
Popular software for streaming audio and video over the Internet. made by RealNetworks of Seattle, Washington.
Rendering
The process of non-realtime drawing of a picture relying on computer processing speed for graphics and compositing.
Resolution
1. Detail. In digital video and audio, the number of bits (four, eight, 10, 12, etc.) determines the resolution of the digital signal. Four bits yields a resolution of one in 16. Eight bits yields a resolution of one in 256. Ten bits yields a resolution of one in 1,024. Eight bits is the minimum acceptable for broadcast television. 2. A measure of the finest detail that can be seen, or resolved, in a reproduced image. While influenced by the number of pixels in an image (for high definition approximately 2,000 x 1,000, broadcast NTSC TV 720 x 487, broadcast PAL TV 720 x 576), note that the pixel numbers do not define ultimate resolution but merely the resolution of that part of the equipment. The quality of lenses, display tubes, film process and film scanners, etc., used to produce the image on the screen must all be taken into account. This is why a live broadcast of the Super Bowl looks better than a broadcast recorded and played off of VHS, while all are NTSC or PAL.
RGB
The abbreviation for the red, green and blue signals, the primary colours of light (and television). Cameras and telecines have red, blue and green receptors, the TV screen has red, green and blue phosphors illuminated by red, green and blue guns. Much of the picture monitoring in a production centre is in RGB. RGB is digitised with 4:4:4 sampling which occupies 50 percent more data than 4:2:2.

s
SCSI	« top of page
Small computer systems interface. A very widely used high data rate general purpose parallel interface. A maximum of eight devices can be connected to one bus, for example a controller, and up to seven disks or devices of different sorts - Winchester disks, optical disks, tape drives, etc. - and may be shared between several computers. SCSI specifies a cabling standard (50-way), a protocol for sending and receiving commands and their format. It is intended as a device-independent interface so the host computer needs no details about the peripherals it controls. But with two versions (single ended and balanced), two types of connectors and numerous variations in the level of implementation of the interface, SCSI devices cannot "plug and play" on a computer with which they have not been tested. Also, with total bus cabling for the popular single ended configuration limited to 18 feet (6 meters), all devices must be close. SCSI is popular and has continued development over a number of years resulting in the following range of maximum transfer rates: Standard SCSI: 5 Mbps (max.) Fast SCSI: 10 Mbps (max.) Ultra SCSI: 20 Mbps (max.) For each of these there is the 8-bit normal "narrow" bus (1 byte per transfer) or the 16-bit Wide bus (2 bytes per transfer), so Wide Ultra SCSI could transfer data at a maximum rate of 40 Mbps. Note that these are peak rates. Continuous rates will be considerably less. Also, achieving this will depend on the performance of the connected device.
SECAM - Sequential Couleur Avec Mémoire
The television broadcast standard in France, the Middle East, and most of Eastern Europe, SECAM provides for sequential colour transmission and storage in the receiver. The signals used to transmit the colour are not transmitted simultaneously but sequentially line for line. SECAM processes 625 lines, a maximum of 833 pixels per line and 50 Hz picture frequency. SECAM is used as a transmission standard and not a production standard (PAL is typically used). Just to be awkward there are two types of SECAM - V (vertical) and H (horizontal). The countries that first started transmitting in SECAM (France and French-speaking Africa, Russia and the various former Soviet bloc countries) use SECAM-Vertical, the colour coding information being put in the vertical spacering. With the advent of teletext this presented a problem as the text information is also put in the vertical spacering! To allow both the SECAM colour coding system and teletext to be used together the colour coding information was put in the horizontal spacering. All the countries that were in the 'second wave' of SECAM (Greece, Saudi Arabia, Iran, Iraq etc) broadcast in SECAM-Horizontal. SECAM video recorders are basically the same as PAL machines with the appropriate coders fitted with the exception of VHS which, unlike all other formats, can only record either Vertical or Horizontal. Other composite recording systems (1"C, U-matic, BVU etc) record both formats simultaneously. SECAM-H is also known as MESECAM (Middle East SECAM). see also NTSC, PAL
Serial
One bit at a time, along a single transmission path.
Serial digital
Digital information that is transmitted in serial form. Often used informally to refer to serial digital television signals.
Serial digital data interface (SDDI)
A way of compressing digital video for use on SDI-based equipment proposed by Sony. Now incorporated into Serial digital transport interface.
Server (file)
A storage system that provides data files to all connected users of a local network. Typically the file server is a computer with large disk storage which is able to record or send files as requested by the other connected (client) computers - the file server often appearing as another disk on their systems. The data files are typically around a few kilobytes in size and are expected to be delivered within moments of request
Server (video)
A storage system that provides audio and video storage for a network of clients. While there are some analogue systems based on optical disks, most used in professional and broadcast applications are based on digital disk storage. Aside from those used for video on demand (VOD), video servers are applied in three areas of television operation: transmission, post production and news. Compared to general purpose file servers, video severs must handle far more data, files are larger and must be continuously delivered. There is no general specification for video servers and so the performance between models varies greatly according to storage capacity, number of channels, compression ratio and degree of access to store material - the latter having a profound influence. Store sizes are very large, typically up to 500 Gigabytes or more. Operation depends entirely on connected devices, edit suites, automation systems, secondary servers, etc., so the effectiveness of the necessary remote control and video networking is vital to success.
Stream
1. To transmit multimedia files that begin playing upon arrival of the first packets, without needing to wait for all the data to arrive. 2. To send data in such a way as to simulate real-time delivery of multimedia. Streaming media: Multimedia content - such as video, audio, text, or animation - that is displayed by a client a client as it is received from the Internet, broadcast network, or local storage.
Sweetening
Electronically improving the quality of an audio or video signal, such as by adding sound effects, laugh tracks, and captions.
Synchronous
A transmission procedure by which the bit and character stream are slaved to accurately synchronised clocks, both at the receiving and sending end.

t
T1	« top of page
In telecommunications, the paired cable used to transport DS1 service.
Tearing
A lateral displacement of the video lines due to sync instability. Visually it appears as though parts of the images have been torn away.
Time Codes
All broadcast tape formats have time code. The time code is generated internally by the machine and recorded along with the picture and sound and is used to identify each individual frame of video recorded. Time code is displayed as hours : minutes : second : frames and is recorded in two different locations - a dedicated, longitudinal audio track - Linear Time Code (LTC) and in the vertical spacering interval - Vertical Interval Time Code (VITC). Recording the time code in two locations allows the time code to be read when the tape is being shuttled at high speed (LTC) or when it is in freeze-frame (VITC). The LTC and the VITC should always match. There is a third type of time code that is used for viewing and logging of tape - Burnt In Time Code (BITC) - sometimes referred to as Time Code In Vision (TCIV) - this is not generated as a matter of course by any format and needs to be 'inserted'. The time code generator on VT recorders can be set to generate all sorts of numbers - some identify roll numbers, some time of day and in the case of most programme dubs running time. For PAL and SECAM time code counts up to 25 frames and then starts again at frame 1 when the second changes, NTSC time code is slightly different - it comes in two types - drop frame and non-drop frame! Non-drop frame counts up to 30 frames and starts again at 1 when the second changes - this is slightly inaccurate however as the actual field rate is 59.94 per second (29.97 frames) so in drop frame a frame is dropped occasionally to keep the count accurate.
Timeline
In nonlinear editing, the area in which audio and video clips are applied, typically giving duration in frames and seconds. Also seen in animation and composition software.
Transcode
The process of converting a file or program from one formatter resolution to another.

v
Variable bit rate reduction	« top of page
see compression

w
WAV	« top of page
The Windows-compatible audio file format. The WAV file can be recorded at 11 kHz, 22 kHz, and 44 kHz, and in 8- or 16-bit mono and stereo. see also AIF
Widescreen
Term given to picture displays that have a wider aspect ratio than normal. For example, TV's normal aspect ratio is 4:3 and widescreen is 16:9. Although this is the aspect ratio used by HDTV, widescreen is also used with normal definition systems.
Windows Media Player
Delivers the most popular streaming and local audio and video formats, including ASF, WAV, AVI, MPEG, Quick-Time, and more. Windows Media Player can play anything from low-bandwidth audio to full-screen video.

y
YUV	« top of page
A colour model used chiefly for video signals in which colours are specified according to their luminance - the Y component - and their hue saturation - the U and V components.