C
caption- A textual representation of the audio information in a video program. Captions are usually intended for the hearing impaired, and therefore include additional text to identify the person speaking, offscreen sounds, and so on.
CAV- Constant angular velocity. Refers to rotating disc systems in which the rotation speed is kept constant, where the pickup head travels over a longer surface as it moves away from the center of the disc. The advantage of CAV is that the same amount of information is provided in one rotation of the disc. Contrast with CLV and ZCLV.
Cb, Cr- The components of digital color-difference video signals carrying blue and red color information, where the brightness (Y) has been subtracted from the blue and red RGB signals to create B-Y and R-Y color-difference signals.
CBEMA- Computer and Business Equipment Manufacturers Association.
CBR- Constant bit rate. Data compressed into a stream with a fixed data rate. The amount of compression (such as quantization) is varied to match the allocated data rate, but as a result quality may suffer during high compression periods. In other words, data rate is held constant while quality is allowed to vary. Compare to VBR.
CCI- Copy control information. Information specifying if content is allowed to be copied.
CCIR Rec. 601- A standard for digital video. The CCIR changed its name to ITU-R, and the standard is now properly called ITU-R BT.601.
CD- Short for compact disc, an optical disc storage format developed by Philips and Sony.
CD+G- Compact disc plus graphics. A variation of CD which embeds graphical data in with the audio data, allowing video pictures to be displayed periodically as music is played. Primarily used for karaoke.
CD-DA- Compact disc digital audio. The original music CD format, storing audio information as digital PCM data. Defined by the Red Book standard.
CD-i- Compact disc interactive. An extension of the CD format designed around a set-top computer that connects to a TV to provide interactive home entertainment, including digital audio and video, video games, and software applications. Defined by the Green Book standard.
CD-Plus- A type of Enhanced CD format using stamped multisession technology.
CD-R- An extension of the CD format allowing data to be recorded once on a disc by using dye-sublimation technology. Defined by the Orange Book standard.
CD-ROM XA- CD-ROM extended architecture. A hybrid version of CD allowing interleaved audio and video.
CD-ROM- Compact disc read-only memory. An extension of the Compact disc digital audio (CD-DA) format that allows computer data to be stored in digital format. Defined by the Yellow Book standard.
CDV- A combination of laserdisc and CD which places a section of CD-format audio on the beginning of the disc and a section of laserdisc-format video on the remainder of the disc.
cell command- A Navigation command executed when the presentation of a cell has been completed.
Cell- In DVD-Video, a unit of video anywhere from a fraction of a second to hours long. Cells allow the video to be grouped for sharing content among titles, interleaving for multiple angles, and so on.
CEMA- Consumer Electronics Manufacturers Association. A subsidiary of the Electronics Industry Association (EIA).
CGMS- Copy Guard Management System. A method of preventing copies or controlling the number of sequential copies allowed. CGMS/A is added to an analog signal (such as line 21 of NTSC). CGMS/D is added to a digital signal, such as IEEE 1394.
challenge key- Data used in the authentication key exchange process between a DVD-ROM drive and a host computer, where one side determines if the other side contains the necessary authorized keys and algorithms for passing encrypted (scrambled) data.
channel bit- The bits stored on the disc, after being modulated.
channel data- The bits physically recorded on an optical disc after error-correction encoding and modulation. Because of the extra information and processing, channel data is larger than the user data contained within it.
channel- A part of an audio track. Typically there is one channel allocated for each loudspeaker.
chapter- In DVD-Video, a division of a title. Technically called a part of title (PTT).
chroma (C')- The nonlinear color component of a video signal, independent of the luma. Identified by the symbol C' (where ` indicates nonlinearity) but usually written as C because it's never linear in practice.
chroma subsampling- Reducing color resolution by taking fewer color samples than luminance samples.
chrominance (C)- The color component (hue and saturation) of light, independent of luminance. Technically, chrominance refers to the linear component of video, as opposed to the transformed nonlinear chroma component.
CIE- Commission Internationale de l'Éclairage/International Commission on Illumination.
CIF- Common intermediate format. Video resolution of 352x288.
CIRC- Cross-interleaved Reed Solomon code. An error-correction coding method which overlaps small frames of data.
clamping area- The area near the inner hole of a disc where the drive grips the disc in order to spin it.
closed caption- Textual video overlays that are not normally visible, as opposed to open captions, which are a permanent part of the picture. Captions are usually a textual representation of the spoken audio. In the United States, the official NTSC Closed Caption standard requires that all TVs larger than 13 inches include circuitry to decode and display caption information stored on line 21 of the video signal. DVD-Video can provide closed caption data, but the subpicture format is preferred for its versatility.
CLUT- Color lookup table. An index that maps a limited range color values to a full range of values such as RGB or YUV.
CLV- Constant linear velocity. Refers to a rotating disc system in which the head moves over the disc surface at a constant velocity, requiring that the motor vary the rotation speed as the head travels in and out. The further the head is from the center of the disc, the slower the rotation. The advantage of CLV is that data density remains constant, optimizing use of the surface area. Contrast with CAV and ZCLV.
CMI- Content management information. General information about copy protection and allowed use of protected content. Includes CCI.
codec- Coder/decoder. Circuitry or computer software that encodes and decodes a signal.
color depth- The number of levels of color (usually including luma and chroma) that can be represented by a pixel. Generally expressed as a number of bits or a number of colors. The color depth of MPEG video in DVD is 24 bits, although the chroma component is shared across 4 pixels (averaging 12 actual bits per pixel).
color difference- A pair of video signals that contain the color components minus the brightness component, usually B-Y and R-Y (G-Y is not used, since it generally carries less information). The color-difference signals for a black-and-white picture are zero. The advantage of color-difference signals is that the color component can be reduced more than the brightness (luma) component without being visually perceptible.
Color model- Any of several means of specifying colors according to their individual components. See RGB, YUV.
colorburst- See burst.
colorist- The title used for someone who operates a telecine machine to transfer film to video. Part of the process involves correcting the video color to match the film.
combo drive- A DVD-ROM drive capable of reading and writing CD-R and CD-RW media. May also refer to a DVD-R or DVD-RW or DVD+RW drive with the same capability.
component video- A video system containing three separate color component signals, either red/green/blue (RGB) or chroma/color difference (YCbCr, YPbPr, YUV), in analog or digital form. The MPEG-2 encoding system used by DVD is based on color-difference component digital video. Very few televisions have component video inputs.
composite video- An analog video signal in which the luma and chroma components are combined (by frequency multiplexing), along with sync and burst. Also called CVBS. Most televisions and VCRs have composite video connectors, which are usually colored yellow.
compression- The process of removing redundancies in digital data to reduce the amount that must be stored or transmitted. Lossless compression removes only enough redundancy so that the original data can be recreated exactly as it was. Lossy compression sacrifices additional data to achieve greater compression.
constant data rate or constant bit rate- See CBR.
Content Scrambling System (CSS)- In DVD-Video, an encryption scheme designed to protect copyrighted material that resides on a disc by periodically scrambling the data using encryption keys.
contrast- The range of brightness between the darkest and lightest elements of an image.
control area- A part of the lead-in area on a DVD containing one ECC block (16 sectors) repeated 192 times. The repeated ECC block holds information about the disc.
CP_SEC- Copyright Protection System flag. In DVD-Video, a 1-bit value stored in the CPR_MAI that indicates if the corresponding sector has implemented a copyright protection system. See Content Scrambling System (CSS).
CPM- Copyrighted Material flag. In DVD-Video, a 1-bit value stored in the CPR_MAI that indicates if the corresponding sector includes any copyrighted material.
CPPM- Content Protection for Prerecorded Media. Copy protection for DVD-Audio.
CPR_MAI- Copyright Management Information. In DVD-Video, an extra 6 bytes per sector that includes the Copyright Protection System Type (CPS_TY) and Region Management information (RMA) in the Contents provider section of the Control data block; and Copyrighted Material flag (CPM), Copyright Protection System flag (CP_SEC) and Copy Guard Management System (CGMS) flags in the Data Area.
CPRM- Content Protection for Recordable Media. Copy protection for writable DVD formats.
CPS_TY- Copyright Protection System Type. In DVD-Video, an 8-bit (1 byte) value stored in the CPR_MAI that defines the type of copyright protection system implemented on a disc.
CPSA- Content Protection System Architecture. An overall copy protection design for DVD.
CPTWG- Copy Protection Technical Working Group. The industry body responsible for developing or approving DVD copy protection systems.
CPU- Central processing unit. The integrated circuit chip that forms the brain of a computer or other electronic device. DVD-Video players contain rudimentary CPUs to provide general control and interactive features.
crop- To trim and remove a section of the video picture in order to make it conform to a different shape. Cropping is used in the pan & scan process, but not in the letterbox process.
CSS- See Content Scrambling System.
CVBS- Composite video baseband signal. Standard single-wire video, mixing luma and chroma signals together.
Cyclic Redundancy Check (CRC)- A method for computing a signature of a sequence of bytes used to detect the presence of errors in the data.
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