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Glossary of DVD Terminology "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 centre 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 colour-difference video signals carrying blue and red colour information, where the brightness (Y) has been subtracted from the blue and red RGB signals to create B-Y and R-Y colour-difference signals. (See Chapter 3.)

CBEMA - Computer and Business Equipment Manufacturers Association. (See Appendix C.)

CBR - Constant bit rate. Data compressed into a stream with a fixed data rate. The amount of compression (such as quantisation) 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.

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.

cDVD - DVD-Video content stored on a CD (or CD-R/RW). Also called mini DVD. Most consumer DVD players can't play a cDVD.

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 - A part of an audio track. Typically there is one channel allocated for each loudspeaker

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.

Cchapter - In DVD-Video, a division of a title. Technically called a part of title (PTT).

Chroma (C´) - The nonlinear colour component of a video signal, independent of the luma (Luminance). Identified by the symbol C´ (where ´ indicates nonlinearity) but usually written as C because it’s never linear in practice.

Chroma sub sampling - Reducing colour resolution by taking fewer colour samples than luminance samples. (See 4:1:1 and 4:2:0.)

Chrominance (C) - The colour component (hue and saturation) of light, independent of luminance. Technically, chrominance refers to the linear component of video, as opposed to the transformed non-linear chroma component.

CIE - Commission Internationale de l’Éclairage/International Commission on Illumination. (See Appendix C.)

CIF - Common Intermediate Fformat. 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 ‘CC’- 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 - Colour lookup table. An index that maps a limited range colour 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 centre of the disc, the slower the rotation. The advantage of CLV is that data density remains constant, optimising use of the surface area. Contrast with CAV and ZCLV.

CMF - Cutting master format. Specification for storing information needed for full DVD mastering (including CSS protection) in the control area of a DVD-R(A) disc. See also DDP.

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.

Colour depth - The number of levels of colour (usually including luma and chroma) that can be represented by a pixel. Generally expressed as a number of bits or a number of colours. The colour depth of MPEG video in DVD is 24 bits, although the chroma component is shared across 4 pixels (averaging 12 actual bits per pixel).

Colour difference - A pair of video signals that contain the colour components minus the brightness component, usually B-Y and R-Y (G-Y is not used, since it generally carries less information). The colour-difference signals for a black-and-white picture are zero. The advantage of colour-difference signals is that the colour component can be reduced more than the brightness (luma) component without being visually perceptible.

Colourburst - See burst.

Colourist - The title used for someone who operates a telecine machine to transfer film to video. Part of the process involves correcting the video colour 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. (Also see RAMbo).

Component video - A video system containing three separate colour component signals, either red/green/blue (RGB) or chroma/colour difference (YCbCr, YPbPr, YUV), in analog or digital form. The MPEG-2 encoding system used by DVD is based on colour-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 coloured 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.

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.

CPPM - Content Protection for Prerecorded Media. Copy protection for DVD-Audio.

CPRM - Content Protection for Recordable Media. Copy protection for writable DVD formats.

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 Protection – DVD Content protection technology
- Composite video baseband signal. Standard single-wire video, mixing luma and chroma signals together.