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1-0
3:2 pull-down
A method for overcoming the incompatibility of film and video frame rates when converting or transferring film
(shot at 24 frames per second) to video (shot at 30 frames per second).
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A
A-B Rolls
A technique in which audio/video information is played
back from two videotape machines rolled sequentially, often for the purpose of dubbing the sequential information
onto a third tape, usually a composite master.
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AC coefficient
Any discrete cosine transform coefficient for which the frequency in one or both dimensions is non- zero.
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Active video lines
All video lines not occurring in the horizontal and vertical blanking intervals.
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Aliasing
Any discrete cosine transform coefficient for which the frequency in one or both dimensions is non- zero.
Undesirable visual effects (sometimes called artifacts) in computer- generated images, caused by inadequate sampling
techniques. The most common effect is jagged edges along diagonal or curved object boundaries.
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Analog
The representation of numerical values by physical variables such as voltage, current, etc.; continuously variable
quantities whose values correspond to the quantitative magnitude of the variables.
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Analog-to-digital converter
An electronic device that converts analog signals to digital form.
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Analog video
A video signal represented by an infinite number of smooth gradations between given video levels. By contrast,
a digital video signal assigns a finite set of levels. See also digital video.
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Animation
The process of displaying a sequential series of still images to achieve a motion effect.
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Anti-aliasing
Software adjustment to make diagonal or curved lines appear smooth and continuous in computer-generated images.
See also aliasing.
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Aspect ratio
The measurement of a film or television viewing area in terms of relative height and width. The aspect ratio of
most modern motion pictures varies between 3:5 to as large as 3:7, which creates a problem when a wide-format motion
picture is transferred to the more square-shaped television screen, with its aspect ratio of 3:4.
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B
Backward compatibility
The ability of a new coding standard to be handled by existing decoders.
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Backward motion vector
A motion vector used for motion compensation from a reference picture that occurs later in display order.
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Bandwidth
The range of signal frequencies that a piece of audio or video equipment can encode or decode; the difference between
the limiting frequencies of a continuous frequency band. Video uses higher frequency than audio, thus requires
a wider bandwidth.
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Betacam
A half-inch video recording format developed by Sony that offers near one-inch tape quality on a portable system.
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Bit depth
The number of bits used to describe the color of each pixel on a computer display. For example, a bit depth of
two means that the monitor can display only black and white pixels; a bit depth of four means the monitor can display
16 different colors; a bit depth of eight allows for 256 colors; and so on.
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Bitrate
The rate at which a storage medium delivers a compressed bitstream to a decoder's input.
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Blank or blanking interval
A period in which no video signal is received by a monitor, while the videodisc or digital video player searches
for the next video segment or frame to display.
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Block
An 8-row by 8-column matrix of pels, or 64 discrete cosine transform coefficients (source, quantized or dequantized).
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Bottom field
One of two fields that comprise a frame of interlaced video. The lines of the top and bottom fields alternate on
a screen, so that each line of a bottom field is located immediately below the corresponding line of the top field.
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B-Picture (Bidirectionally predictive-coded
picture)
A picture that is coded using motion compensated prediction from past and/or future reference pictures. See also
motion compensation.
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Broadcast quality
In the US, a standard of 525 lines of video picture information at a rate of 60 Hz. See NTSC format.
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Byte aligned
A bit in a coded bitstream that is located a multiple of 8 bits from the first bit in the stream.
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C
CBT (Computer-based training)
The use of a computer to deliver instruction or training; also known as Computer-Aided (or assisted) Instruction
(CAI), Computer-Aided Learning (CAL), Computer-Based Instruction (CBI), and Computer- Based Learning (CBL).
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CCITT
Comité Consultatif International de Télécommunications et Télégraphie. This
committee of the International Telecommunications Union makes technical recommendations about telephone and data
communication systems. Plenary sessions are held every four years to adopt new standards.
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CD (Compact Disc or compact audio disc)
A 4.75-inch (12cm) optical disc that contains information (usually musical) encoded digitally in the constant linear
velocity (CLV) format. This popular format for high-fidelity music offers 90 dB signal/noise ratio, 74 minutes
of digital sound, and no degradation of quality from playback. The standards for this format (developed by NV Philips
and Sony Corporation) are known as the Red Book.
The official (and rarely used) designation for the audio-only format is CD-DA (compact disc-digital audio). The
simple audio format is also known as CD-A (compact disc-audio). A smaller (3") version of the CD is known
as CD-3.
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CD+G (Compact Disc-Graphics)
A CD format that includes extended graphics capabilities as written into the original CD-ROM specifications. Includes
limited video graphics encoded into the CD subcode area. Developed and marketed by Warner New Media.
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CD-i (Compact Disc-Interactive)
A compact disk format released in October 1991 that provides audio, digital data, still graphics, and motion video.
The standards for this format (developed by NV Philips and Sony Corporation) are known as the Green Book.
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CD+MIDI (Compact Disc-Musical Instrument Digital
Interface)
A CD format that adds to the CD+G formats digital audio, graphics information, and musical instrument digital interface
(MIDI) specifications and capabilities. Developed and marketed by Warner New media.
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CD-ROM (Compact Disc-Read Only Memory)
A 4.75-inch laser-encoded optical memory storage medium with the same constant linear velocity (CLV) spiral format
as audio CDs and some videodiscs, CD-ROMs can hold about 550 megabytes of data. CD-ROMs require more error-correction
information than the standard prerecorded compact audio disc.
The standards for this format (developed by NV Philips and Sony Corporation) are known as the Yellow Book. See
also CD-ROM XA.
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CD-ROM drive or CD-ROM player
A device that retrieves data from a CD-ROM disc; differs from a standard audio CD player by the incorporation of
additional error-correction circuitry. CD-ROM drives usually can also play music from audio CDs.
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CD-ROM XA
(Compact Disc-Read-Only Memory Extended Architecture)
An extension of the CD-ROM standard billed as a hybrid of CD-ROM and CD- i, and promoted by Sony and Microsoft.
The extension adds ADPCM audio from CD-i and permits the interleaving of sound and video data for animation and
sound synchronization.
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CD Video
A CD format introduced in 1987 that combined 20 minutes of digital audio and six minutes of analog video
on a standard 4.75-inch CD. Upon introduction, many firms renamed 8- inch and 12-inch videodiscs as CDV, in an
attempt to capitalize on the consumer popularity of the audio CD. The term fell out of use in 1990 and was replaced
in some part by laserdisc.
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CD-WO (Compact Disc-Write Once)
A variant on CD-ROM that can be written to once and read many times; developed by NV Philips and Sony Corporation.
Also known as CD-WORM (CD-write once/read many). Standards for this format are known as the Orange Book.
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Chroma format
Defines the number of chrominance blocks in a macroblock.
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Chrominance
Portion of a video signal that carries color information (hue and saturation, but not brightness). A matrix, block,
or single pel represents one of the two color-difference signals related to the primary colors as defined in the
bitstream. The symbols used for the color difference signals are Cr and Cb. See also YCbCr.
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CIF (Common Image Format)
The standard sample structure that represents the picture information of a single frame in digital HDTV, independent
of frame rate and sync/blank structure. The uncompressed bit rate for transmitting CIF at 29.97 frames/sec is 36.45
Mbps.
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Coded order
The order in which pictures are stored and decoded. This order is not necessarily the same as the display order.
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Coding parameters
The set of user-definable parameters that characterize a coded video bitstream. While bitstreams are characterized
by coding parameters, decoders are characterized by the bitstreams they are capable of decoding.
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Component
A matrix, block, or single pel from one of the three matrices (one for luminance and two for chrominance) that
make up a picture.
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Component video
The separation of chrominance (color) and luminance parts of the video signal. In component video, these two signals
are recorded separately, which helps maintain better picture quality over more generations.
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Composite video
The complete visual wave form of the color video signal composed of chrominance and luminance picture information;
blanking pedestal; field, line, and color sync pulses; and field equalizing pulses. See also RGB.
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Compression ratio
The size of the original image divided by the size of the compressed image, measuring the degree to which a compression
routine can reduce the size of a file.
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Constant bitrate
Operation in which the bitrate is constant from start to finish of a compressed bitstream.
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Constant bitrate coded video
A compressed video bitstream with a constant average bitrate.
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Courseware
Instructional software, including all discs, tapes, books, charts, and computer programs necessary to deliver a
complete instructional module or course.
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CRC (cyclic redundancy code)
A code used for error detection and correction.
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D
D1 and D2
Digital tape component format (D1) and digital tape composite format (D2) used for professional video recording.
Both can go through multiple generations of dubbing without visible loss of picture quality.
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D/A (digital to analog)
The conversion of digital signals to analog form.
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DAC (Digital/Analog Converter)
Device that converts digital signals to analog form.
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Data partitioning
A method for dividing a bitstream into two bitstreams for error resilience. The two bitstreams must be recombined
before decoding.
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dB (Decibel)
A logarithmic measure of the ratio between two powers, voltages, currents, sound intensities, etc. Signal-to-noise
ratios are expressed in decibels.
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DC coefficient
The DCT coefficient for which the frequency is zero in both dimensions.
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DCT (Discrete Cosine Transform)
A compression technique in which data is digitized, then put through a process of intraframe coding and interframe
coding, enabling the system to transmit the first image and thereafter only transmit the differences from one frame
to the next. See lossy compression.
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DCT coefficient
The amplitude of a specific cosine basis function. See DCT.
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Decoder input buffer
The first-in-first-out (FIFO) buffer specified in a video buffering verifier.
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Decoder input rate
The data rate specified in a video buffering verifier and encoded in the coded video bitstream.
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Decoding
A process that converts an input coded bitstream into pictures or audio samples.
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Dequantization
The process of rescaling quantized DCT coefficients after their representation in the bitstream has been decoded
and before they are presented to the inverse DCT.
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Digital video
A video represented by computer-readable binary numbers that describe a finite set of colors and luminance levels.
See analog video.
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Disc
Flat, circular, rotating medium that can store various types of information, both analog and digital. "Disc"
is often used in reference to optical storage media, while "disk" refers to magnetic storage media. Disc
is often used as a short form for videodisc or compact audio disc (CD).
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Disk
Alternative spelling for "disc" that generally refers to magnetic storage medium on which information
can be accessed at random. Floppy disks and hard disks are examples.
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Display order
The order in which decoded pictures are displayed. Normally this is the same order in which the pictures entered
the encoder.
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Dithering
A process that improves the perceived quality of a screen graphic when the color palette is reduced. For example,
when converting from 24-bit color to 8-bit color (an 8-bit palette has only 256 colors compared to the 24-bit palette's
millions), dithering adds pixels of different colors to simulate the original color. Dithering is also known as
"error diffusion."
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Dual-channel audio
The ability to reproduce two audio channels, playing them either simultaneously or independently; a characteristic
of all optical videodisc systems.
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DYUV or delta-YUV
An efficient color-coding scheme for natural pictures used in CD-i. The human eye is less sensitive to color variations
than to intensity variations, so DYUV encodes luminance (Y) information at full bandwidth and chrominance (UV)
information at half bandwidth or less, storing only the differences (deltas) between each value and the one following
it.
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E
EACEM
European Association of Consumer Electronics Manufacturers.
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Encryption
A procedure for encoding data that makes it difficult to decode the data without proprietary software of hardware.
This procedure protects data or software from unauthorized access or use.
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Entropy
The average amount of information represented by a symbol in a message. Entropy is a function of the model used
to produce the message and can be reduced by increasing the complexity of the model to better reflect the distribution
of source symbols in the original message. Because entropy is a measure of the information contained in a message,
it represents the lower bound for compression.
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F
Field
The set of alternating lines in an interlaced video frame. An interlaced frame consists of two fields -- a top
field and a bottom field. A field is one-half of a complete television scanning cycle (1/60 of a second in
NTSC; 1/50 of a second in PAL/SECAM). When interlaced, two fields combine to make one video frame.
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Field/frame synchronization
The elimination of video and film frame ambiguity by the use of the full-frame identification process during film-to-tape
transfer.
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Field frequency
The rate at which a complete field is scanned or displayed, normally 59.94 times per second in NTSC.
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Field period
The reciprocal of twice the frame rate.
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Film chain
A term used to encompass the total grouping of equipment used to transfer slide or movie film picture frames to
electronic picture frames; usually consists of film and slide projectors, a multiplexer and a television camera.
Also known as telecine.
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Flag
A variable that can take one of only two values. See also parameter.
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Flicker
Video effect (usually unwanted) on a still or frozen frame caused when two fields that combine to make the frame
are not identically matched, thus creating two different pictures alternating every 1/60 of a second. Interfield
flicker can occur when field dominance is incorrectly specified or if field dominance changes at one or more points
on the master tape from having been edited on equipment that is incapable of frame-accurate editing. Also known
as jitter or jutter. See also interfield frames.
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Forbidden
When used in the clauses defining a coded bitstream, indicates that the value must never be used. This restriction
is usually applied to avoid emulation of start codes.
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Forced updating
The process by which macroblocks are occasionally intra coded to ensure that mismatch errors between the inverse
DCT processes in encoders and decoders cannot build up excessively.
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Forward compatibility
The ability of a coding standard that works with existing decoders to work with new decoders.
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Forward motion vector
A motion vector used for motion compensation from a reference picture that comes at an earlier time in display
order.
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Frame
A single, complete picture in a video or film recording. A video frame consists of two interlaced fields of either
525 lines (NTSC) or 625 lines (PAL/SECAM), running at 30 frames per second (NTSC) or 25 fps (PAL/SECAM). Film runs
at 24 fps.
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Frame buffer
1. A device capable of storing all 525 lines of a television frame and functioning as a time-base corrector.
2. A memory device that stores, pixel by pixel, the contents of an image. Frame buffers are used to refresh a raster
image. Sometimes they incorporate local processing ability. The "depth" of the frame buffer is the number
of bits per pixel, which determines the number of colors or intensities that can be displayed.
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Frame period
The reciprocal of the frame rate.
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Frame rate
The speed at which video frames are scanned or displayed -- 30 frames a second for NTSC, 25 frames per second for
PAL/SECAM.
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Freeze-frame
A single frame from a segment of video or film footage held motionless on the screen. Unlike a still frame, a freeze-frame
is not a picture intended to appear motionless, but is one frame taken from a longer motion sequence.
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Full-frame time code
A standardized SMPTE method of address-coding a videotape that retains all frame numbers in chronological order,
resulting in a slight deviation from clock time.
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Full-motion video
A video sequence displayed at full television standard resolutions and frame rates. In the US, this would equate
to NTSC video at 30-frames-per-second.
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Future reference picture
A reference picture that occurs at a later time than the current picture in display order.
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G
Gamma
A display characteristic of CRTs defined by: Light = Volts ^ gamma where gamma is 2.35 plus or minus 0.1. CRTs
usually have values between 2.25 and 2.45, and 2.35 is a common value. No direct-view CRTs have values lower than
2.1. CRT projectors exhibit different values; green tubes are typically at 2.2, while red is usually around 2.1,
and blue can be as low as 1.7. Pictures destined for display on CRTs are gamma-corrected, meaning that a transfer
characteristic has been applied to correct for the CRT gamma.
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Users of TV cameras have to accept the gamma characteristic supplied by the manufacturer, except for broadcasters
who are able to adjust the curves that profile gamma correction. In this case video engineers adjust the gamma
correction until they like the look of the picture on the studio monitor. Even so, no TV camera uses a true gamma-correction
curve; cameras all use flattened curves with a maximum slope near black of between 3 and 5. The higher the slope,
the better the colorimetry but the worse the noise performance.
Genlocking
The process of aligning the data rate of a video image with that of a digital device to digitize the image and
enter it into computer memory. The machine that performs this function is known as a genlock.
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H
Hangover
Audio data transmitted after a silence detector indicates that no audio data is present. Hangover ensures that
the ends of words, important for comprehension, are transmitted even though they are often of low energy.
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HDTV (High-definition television)
Any one of a variety of video formats offering greater visual accuracy (or resolution) than current NTSC, PAL,
or SECAM broadcast standards. Current formats generally range in resolution from 655 to 2,125 scanning lines, having
an aspect ration of 5:3 (or 1.67:1), and a video bandwidth of 30 to 50 MHz (5+ times greater than NTSC standard).
Digital HDTV has a bandwidth of 300 MHz. HDTV is subjectively comparable to 35 mm film.
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Header
A block of data in a coded bitstream containing information about the data that follows.
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Hi8 Video
The high-quality extension of the Video 8 (or 8mm) format, which features higher luminance resolution.
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High Sierra format
A standard format for placing files and directories on CD-ROMs proposed by an ad hoc committee of computer vendors,
software developers, and CD-ROM system integrators. (Work on the format proposal began at the High Sierra Hotel
at Lake Tahoe, Nevada.) A revised version of the format was adopted by the International Standards Organization
as ISO 9660.
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Hybrid Coder
The basis for international standards for videotelephony and the prototype compression technique from which MPEG
was designed. In the archetypal hybrid coder, an estimate of the next frame to be processed is formed from the
current frame; the difference is then encoded by some purely intraframe mechanism. In recent years, the most attention
has been paid to coders that include motion compensation, in which the estimate is formed by a two-dimensional
warp of the previous frame, and the difference is encoded using a block transform (the Discrete Cosine Transform).
The key feature of the hybrid coder is the presence of a complete decoder within it. The decoder processes the
difference between the current frame as represented at the receiver and the incoming frame. The receiver must therefore
track the transmitter precisely, meaning that the decoders at the receiver and transmitter must match. The system
is sensitive to channel errors and does not permit random access. However, it is on the order of three to four
times as efficient as coders that use no prediction.
In practice, this coder is modified to suit specific applications. The standard telephony model uses a forced update
of the decoded frame so that channel errors do not propagate. When a participant enters the conversation late or
alternates between image sources, for example, residual errors die out and a clear image is obtained after a few
frames. Similar techniques are used in versions of this coder developed for direct satellite television broadcasting.
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Hybrid scalability
Hybrid scalability is the combination of two or more types of scalability.
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Hz (Hertz)
The standard unit of frequency. One Hz equals one cycle (or vibration) per second. One kilohertz (KHz) equals 1,000
cycles per second, and one megahertz (MHz) equals 1,000,000 cycles per second. This standard unit is named after
German physicist Heinrich Hertz (1857-1894).
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I
Intellectual property
Creative content that can be protected by either copyright or patent law. With the proliferation of digital transmission
of content without monitoring, intellectual property rights, protection, and compensation have become hotly debated
topics in the multimedia arena.
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Interfield frames
A product of the 3:2 pull-down, film-to-tape transfer process, in which the video frame is composed of two fields,
each of a different film frame. These mixed fields do not interfere with normal viewing, but on a videodisc --
where a viewer can freeze on any single frame -- an interfield frame might produce unwanted flicker.
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Interframe coding
In video signal transmission, a way to compress the video signal that concentrates on coding high-detail areas
of a picture at the expense of the less detailed areas.
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Interlace
The pattern described by two separate field scans when they join to form a complete video frame. As the video picture
is transmitted, the first field picks up even-numbered scan lines - the second, odd-numbered ones. The two interleave
together to form a single, complete frame.
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Intra coding
Coding of a macroblock or picture that uses information only from that macroblock or picture.
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Intraframe coding
A way to compress a video signal for transmission in which half the picture information is eliminated by discarding
every other frame as it comes from the camera. During playback, each frame remains on the screen twice the normal
duration to simulate the standard 30-frames-per- second video rate.
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I Picture (Intra-coded picture)
A picture coded using information only from the picture.
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J
JPEG (Joint Photographic Experts Group)
The international consortium of hardware, software, and publishing interests who, under the auspices of the International
Standards Organization, has defined a universal standard for digital compression and decompression of still images
for use in computer systems (commonly called "JPEG" or "JPEG-Standard") JEPG compresses at
about a 20:1 ratio before visible image degradation occurs.
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K
Keyer
Signal processing device that cuts a hole in the background video and fills in the hole from a different video
source, e.g., computer-generated text and graphics keyed over NTSC video.
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L
Letterboxing
A technique for displaying movies on video in the original aspect ratio of the theater, resulting in the apparent
cropping of the top and bottom of the screen. The technique accommodates program material that has a wide picture
aspect ratio.
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Level
A defined set of constraints on the values that may be taken by some parameters within a profile. A profile can
contain one or more levels.
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Lossless compression
A compression technique that preserves all the original information in an image or other data structures.
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Lossy compression
A compression technique that achieves optimal data reduction by discarding redundant and unnecessary information
in an image. See DCT.
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LSI (Large Scale Integration)
Large Scale Integration means generally more than 1,000 and less than 10,000 components on a computer chip.
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Luma (Y)
One of the coefficients in composite video. Video originates with linear-light (tristimulus) RGB primary components,
conventionally contained in the range 0 (black) to +1 (white). From the RGB triple, three gamma-corrected primary
signals are computed; each is essentially the 0.45-power of the corresponding tristimulus value, similar to a square-root
function.
Although television primaries have changed over the years since the adoption of the NTSC standard in 1953, the
coefficients of the luma equation for 525- and 625-line video have remained unchanged. For HDTV, the primaries
are different, and the luma coefficients have been standardized with somewhat different values.
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M
Macroblock
The four 8 x 8 blocks of luminance data and the corresponding 8 x 8 blocks of chrominance data coming from a 16
x 16 section of a picture's luminance component. The number of chrominance blocks is two for 4:2:0 chroma format,
four for 4:2:2 chroma format, or eight for 4:4:4 chroma format. The term "macroblock" is sometimes used
to refer to pel data and sometimes to the coded representation of the pel values and other data elements defined
in the macroblock header. The usage should be clear from the context.
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Master
An original audio tape, videotape or film; used for broadcast or to make copies.
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Motion compensation
The use of motion vectors to improve the efficiency of predicting pel values. The motion vectors provide offsets
into past and/or future reference pictures containing previously decoded pel values that are used to form the prediction
error signal.
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Motion estimation
The process of estimating motion vectors during the encoding process.
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Motion vector
A two-dimensional vector used for motion compensation that provides an offset from the coordinate position in the
current picture to the coordinates in a reference picture.
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MPC (Multimedia Personal
Computer)
A trademarked abbreviation for Multimedia Personal Computer. The original MPC specification was developed by Tandy
Corporation and Microsoft as the minimum platform capable of running multimedia software. In the Summer of 1995,
the MPC Marketing Council introduced an upgraded MPC 3 standard.
The MPC 1 Specification defines the following minimum standard requirements: a 386SX or 486 CPU; 2 MB RAM; 30 MB
hard disk; VGA video display; 8-bit digital audio subsystem; CD-ROM drive; and systems software compatible with
the applications programming interfaces (APIs) of Microsoft Windows Version 3.1 or higher.
The MPC 2 Specification defines the following minimum standard requirements: 25 MHz 486SX with 4 MB RAM; 160 MB
hard disk; 16-bit sound card; 65,536 color video display; double-speed CD-ROM drive; and systems software compatible
with the applications programming interfaces (APIs) of Microsoft Windows Version 3.1 or higher.
The MPC 3 Specification defines the following minimum standard requirements: 75 MHz Pentium with 8 MB RAM; 540
MB hard disk; 16-bit sound card; 65,536 color video display; quad speed CD-ROM drive; OM-1 complaint MPEG-1 video,
and systems software compatible with the applications programming interfaces (APIs) of Microsoft Windows Version
3.1 and DOS 6.0 or higher.
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MPEG (Motion Picture Experts Group)
A working committee which, under the auspices of the International Standards Organization, has defined standards
for the digital compression and decompression of motion video/audio for use in computer systems. These standards
consist of MPEG-1 and MPEG-2.
The MPEG-1 standard delivers decompression data at 1.2 to 1.5 MB per second, allowing CD players to play full-motion
color movies at 30 frames per second. MPEG-1 compresses at about a 50:1 ratio before image degradation occurs,
but compression ratios as high as 200:1 are attainable. Building on the MPEG-1 standard is MPEG-2, which extends
to the higher data rates (2-15 Mbps) needed for signals delivered from remote sources (such as broadcast, cable,
or satellite). MPEG-2 is designed to support a range of picture aspect ratios, including 4:3 and 16:9.
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N
NAB (National Association
of Broadcasters)
National Association of Broadcasters.
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NOISE
Random electrical energy or interference. In video, noise can produce a random salt-and-pepper pattern over the
picture. Heavy video noise is called snow.
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Nondrop-frame time code
See full-frame time code.
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Non-intra coding
Coding of a macroblock (or picture) that uses information from both that macroblock and from macroblocks occurring
at other times.
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NTSC (National Television
Systems Committee)
National Television Systems Committee of the Electronics Industries Association (EAI) which prepared the NTSC format
specifications approved by the Federal Communications Commission, in December 1953, for US commercial color broadcasting.
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