D
DAC- Digital-to-analog converter. Circuitry that converts digital data (such as audio or video) to analog data.
DAE- Digital audio extraction. Reading digital audio data directly from a CD audio disc.
DAT- Digital audio tape. A magnetic audio tape format that uses PCM to store digitized audio or digital data.
data area- The physical area of a DVD disc between the lead in and the lead out (or middle area) which contains the stored data content of the disc.
data rate- The volume of data measured over time; the rate at which digital information can be conveyed. Usually expressed as bits per second with notations of kbps (thousand/sec), Mbps (million/sec), and Gbps (billion/sec). Digital audio date rate is generally computed as the number of samples per second times the bit size of the sample. For example, the data rate of uncompressed 16-bit, 48-kHz, two-channel audio is 1536 kbps. Digital video bit rate is generally computed as the number of bits per pixel times the number of pixels per line times the number of lines per frame times the number of frames per second. For example, the data rate of a DVD movie before compression is usually 12 x 720 x 480 x 24 = 99.5 Mbps. Compression reduces the data rate. Digital data rate is sometimes inaccurately equated with bandwidth.
Data Search Information (DSI)- Information for Fast Forward/Fast Backward and seamless playback. This is real time control data spread throughout the DVD-Video data stream. Along with PGCI, these packets are part of the 1.00 mbit/sec overhead in video applications (Book B). These packets contain navigation information which makes it possible to search and maintain seamless playback of the Video Object Unit (VOBU). The most important field in this packet is the sector address where the first reference frame of the video object begins. Advanced angle change and presentation timing are included to assist seamless playback.
dB- See decibel.
DBS- Digital broadcast satellite. The general term for 18-inch digital satellite systems.
DC- Direct current. Electrical current flowing in one direction only. Adopted in the video world to refer to a signal with zero frequency. Compare to AC.
DCC- Digital compact cassette. A digital audio tape format based on the popular compact cassette. Abandoned by Philips in 1996.
DCT- Discrete cosine transform. An invertible, discrete, orthogonal transformation. Got that? A mathematical process used in MPEG video encoding to transform blocks of pixel values into blocks of spatial frequency values with lower-frequency components organized into the upper-left corner, allowing the high-frequency components in the lower-right corner to be discounted or discarded. Also digital component technology, a videotape format.
DDWG- Digital Display Working Group (see DVI).
decibel (dB)- A unit of measurement expressing ratios using logarithmic scales related to human aural or visual perception. Many different measurements are based on a reference point of 0 dB; for example a standard level of sound or power.
decimation- A form of subsampling which discards existing samples (pixels, in the case of spatial decimation, or pictures, in the case of temporal decimation). The resulting information is reduced in size but may suffer from aliasing.
decode- To reverse the transformation process of an encoding method. Decoding processes are usually deterministic.
decoder- 1) A circuit that decodes compressed audio or video, taking an encoded input stream and producing output such as audio or video. DVD players use the decoders to recreate information that was compressed by systems such as MPEG-2 and Dolby Digital; 2) a circuit that converts composite video to component video or matrixed audio to multiple channels.
delta picture (or delta frame)- A video picture based on the changes from the picture before (or after) it. MPEG P pictures and B pictures are examples. Contrast with key picture.
deterministic- A process or model whose outcome does not depend upon chance, and where a given input will always produce the same output. Audio and video decoding processes are mostly deterministic.
digital signal processor (DSP)- A digital circuit that can be programmed to perform digital data manipulation tasks such as decoding or audio effects.
Digital Versatile Disc (DVD)- Generic name for a family of related disc formats encompassing Video, Audio, and computer file storage on an optical disc format. They share common physical format and logical/file structures. They differ only content. Physical differences between erasable (Book E), write-once read many times (Book D), and ROM (Book A) may emerge.
digital video noise reduction (DVNR)- Digitally removing noise from video by comparing frames in sequence to spot temporal aberrations.
digital- Expressed in digits. A set of discrete numeric values, as used by a computer. Analog information can be digitized by sampling.
Digital Visual Interface (DVI)- The digital video interface standard developed by the Digital Display Working Group (DDWG). A replacement for analog VGA monitor interface.
digitize- To convert analog information to digital information by sampling.
DIN- Deutsches Institut für Normung/German Institute for Standardization.
directory- The part of a disc that indicates what files are stored on the disc and where they are located.
Directory structure- For the video specification (Book B), this defines a common set of files that must be present on all DVD discs. Components include Root and VIDEO_TS.
DirectShow- A software standard developed by Microsoft for playback of digital video and audio in the Windows operating system. Replaces the older MCI and Video for Windows software.
disc key- A value used to encrypt and decrypt (scramble) a title key on DVD-Video discs.
disc menu- The main menu of a DVD-Video disc, from which titles are selected. Also called the system menu or title selection menu. Sometimes confusingly called the title menu, which more accurately refers to the menu within a title from which audio, subpicture, chapters, and so forth can be selected.
discrete cosine transform (DCT)- An invertible, discrete, orthogonal transformation. A mathematical process used in MPEG video encoding to transform blocks of pixel values into blocks of spatial frequency values with lower-frequency components organized into the upper-left corner, allowing the high-frequency components in the lower-right corner to be discounted or discarded.
discrete surround sound- Audio in which each channel is stored and transmitted separate from and independent of other channels. Multiple independent channels directed to loudspeakers in front of and behind the listener allow precise control of the soundfield in order to generate localized sounds and simulate moving sound sources.
display rate- The number of times per second the image in a video system is refreshed. Progressive scan systems such as film or HDTV change the image once per frame. Interlace scan systems such as standard television change the image twice per frame, with two fields in each frame. Film has a frame rate of 24 fps, but each frame is shown twice by the projector for a display rate of 48 fps. 525/60 (NTSC) television has a rate of 29.97 frames per second (59.94 fields per second). 625/50 (PAL/SECAM) television has a rate of 25 frames per second (50 fields per second).
Divx- Digital Video Express. A short-lived pay-per-viewing-period variation of DVD.
DLT- Digital linear tape. A digital archive standard using half-inch tapes, commonly used for submitting a premastered DVD disc image to a replication service.
Dolby Digital- A perceptual coding system for audio, developed by Dolby Laboratories and accepted as an international standard. Dolby Digital is the most common means of encoding audio for DVD-Video and is the mandatory audio compression system for 525/60 (NTSC) discs.
Dolby Pro Logic- The technique (or the circuit which applies the technique) of extracting surround audio channels from a matrix-encoded audio signal. Dolby Pro Logic is a decoding technique only, but is often mistakenly used to refer to Dolby Surround audio encoding.
Dolby Surround- The standard for matrix encoding surround-sound channels in a stereo signal by applying a set of defined mathematical functions when combining center and surround channels with left and right channels. The center and surround channels can then be extracted by a decoder such as a Dolby Pro Logic circuit which applies the inverse of the mathematical functions. A Dolby Surround decoder extracts surround channels, while a Dolby Pro Logic decoder uses additional processing to create a center channel. The process is essentially independent of the recording or transmission format. Both Dolby Digital and MPEG audio compression systems are compatible with Dolby Surround audio.
domain- Program Chains (PGC) are classified into four types of domains, including First Play Domain, Video Manager Menu Domain, VTS Menu Domain and Title Domain.
downmix- To convert a multichannel audio track into a two-channel stereo track by combining the channels with the Dolby Surround process. All DVD players are required to provide downmixed audio output from Dolby Digital audio tracks.
downsampling- See subsampling.
DRC- See dynamic range compression.
driver- A software component that enables an application to communicate with a hardware device.
DSD- Direct Stream Digital. An uncompressed audio bitstream coding method developed by Sony. An alternative to PCM.
DSI- See Data Search Information (DSI).
DSP- Digital signal processor (or processing).
DSVCD- Double Super Video Compact. Long-playing (100-minute) variation of SVCD.
DTS- Digital Theater Sound. A perceptual audio-coding system developed for theaters. A competitor to Dolby Digital and an optional audio track format for DVD-Video and DVD-Audio.
DTS-ES- A version of DTS decoding that is compatible with 6.1-channel Dolby Surround EX. DTS-ES Discrete is a variation of DTS encoding and decoding that carries a discrete rear center channel instead of a matrixed channel.
DTV- Digital television. In general, any system that encodes video and audio in digital form. In specific, the Digital Television System proposed by the ATSC or the digital TV standard proposed by the Digital TV Team founded by Microsoft, Intel, and Compaq.
duplication- The reproduction of media. Generally refers to producing discs in small quantities, as opposed to large-scale replication.
DV- Digital Video. Usually refers to the digital videocassette standard developed by Sony and JVC.
DVB- Digital video broadcast. A European standard for broadcast, cable, and digital satellite video transmission.
DVC- Digital video cassette. Early name for DV.
DVCAM- Sony's proprietary version of DV.
DVCD- Double Video Compact Disc. Long-playing (100-minute) variation of VCD.
DVCPro- Matsushita's proprietary version of DV.
DVDA- DVD Association, a non-profit industry trade association representing DVD authors, producers, and vendors throughout the world.
DVD-Audio (DVD-A)- The audio-only format of DVD. Primarily uses PCM audio with MLP encoding, along with an optional subset of DVD-Video features.
DVD Forum- An international association of hardware and media manufacturers, software firms and other users of Digital Versatile Discs, created for the purpose of exchanging and disseminating ideas and information about the DVD Format.
DVD Multi- DVD Multi is a logo program that promotes compatibility with DVD-RAM and DVD-RW. It is not a drive, but defines a testing methodology which, when passed, ensures the drive product can in fact read RAM and -RW. It puts the emphasis for compatibility on the reader, not the writer.
DVD-R (DVD Recordable)- The authoring use drive (635nm laser) was introduced in 1998 by Pioneer, and the general use format (650nm laser) was authorized by DVD Forum in 2000. DVD-R offers a write-once, read-many storage format akin to CD-R and is used to master DVD-Video and DVD-ROM discs, as well as for data archival and storage applications.
DVD-RW (DVD ReWritable)- A rewritable DVD format, introduced by Pioneer, that is similar to DVD+RW. It has a read-write capacity of 4.38 GB.
DVD-RAM (DVD Random Access Memory)- A rewritable DVD disc endorsed by Panasonic, Hitachi and Toshiba. It is a cartridge-based, and more recently, bare disc technology for data recording and playback. The first DVD-RAM drives were introduced in Spring 1998 and had a capacity of 2.6GB (single sided) or 5.2GB (double sided). DVD-RAM Version 2 discs with 4.38GB arrived in late 1999, and double-sided 9.4GB discs in 2000. DVD-RAM drives typically read DVD-Video, DVD-ROM and CD media. The current installed base of DVD-ROM drives and DVD-Video players cannot read DVD-RAM media.
DVD-ROM- The base format of DVD. ROM stands for read-only memory, referring to the fact that standard DVD-ROM and DVD-Video discs can't be recorded on. A DVD-ROM can store essentially any form of digital data.
DVD+RW (DVD ReWritable)- Developed in cooperation by Hewlett-Packard, Mitsubishi Chemical, Philips, Ricoh, Sony and Yamaha, it is a rewritable format that provides full, non-cartridge, compatibility with existing DVD-Video players and DVD-ROM drives for both real-time video recording and random data recording across PC and entertainment applications.
DVD-Video (DVD-V)- A standard for storing and reproducing audio and video on DVD-ROM discs, based on MPEG video, Dolby Digital and MPEG audio, and other proprietary data formats.
DVI- See Digital Visual Interface.
DVNR- See digital video noise reduction.
DVS- Descriptive video services. Descriptive narration of video for blind or sight-impaired viewers.
dye polymer- The chemical used in DVD-R and CD-R media that darkens when heated by a high-power laser.
dye-sublimation- Optical disc recording technology that uses a high-powered laser to burn readable marks into a layer of organic dye. Other recording formats include magneto-optical and phase-change.
dynamic range compression- A technique of reducing the range between loud and soft sounds in order to make dialogue more audible, especially when listening at low volume levels. Used in the downmix process of multichannel Dolby Digital sound tracks.
dynamic range- The difference between the loudest and softest sound in an audio signal. The dynamic range of digital audio is determined by the sample size. Increasing the sample size does not allow louder sounds; it increases the resolution of the signal, thus allowing softer sounds to be separated from the noise floor (and allowing more amplification with less distortion). Dynamic range refers to the difference between the maximum level of distortion-free signal and the minimum limit reproducible by the equipment.
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