DVD Glossary - Part 1 (A

2-2 pulldown - The process of transferring 24-frame-per-second film to video by repeating each film frame as two video fields. (See Chapter 3 for details.) When 24-fps film is converted via 2-2 pulldown to 25-fps 625/50 (PAL) video, the film runs 4 percent faster than normal.

2-3 pulldown - The process of converting 24-frame-per-second film to video by repeating one film frame as three fields, then the next film frame as two fields. (See Chapter 3 for details.)

3-2 pulldown - An uncommon variation of 2-3 pulldown, where the first film frame is repeated for 3 fields instead of two. Most people mean 2-3 pulldown when they say 3-2 pulldown.

4:1:1 - The component digital video format with one Cb sample and one Cr sample for every four Y samples. 4:1 horizontal downsampling with no vertical downsampling. Chroma is sampled on every line, but only for every four luma pixels (i.e., 1 pixel in a 1 x 4 grid). This amounts to a subsampling of chroma by a factor of two compared to luma (and by a factor of four for a single Cb or Cr component). DVD uses 4:2:0 sampling, not 4:1:1 sampling.

4:2:0 - The component digital video format used by DVD, where there is one Cb sample and one Cr sample for every four Y samples (i.e., 1 pixel in a 2 x 2 grid). 2:1 horizontal downsampling and 2:1 vertical downsampling. Cb and Cr are sampled on every other line, in between the scan lines, with one set of chroma samples for each two luma samples on a line. This amounts to a subsampling of chroma by a factor of two compared to luma (and by a factor of four for a single Cb or Cr component).

4:2:2 - The component digital video format commonly used for studio recordings, where there is one Cb sample and one Cr sample for every two Y samples (i.e., 1 pixel in a 1 x 2 grid). 2:1 horizontal downsampling with no vertical downsampling. This allocates the same number of samples to the chroma signal as to the luma signal. The input to MPEG-2 encoders used for DVD is typically in 4:2:2 format, but the video is subsampled to 4:2:0 before being encoded and stored.

4:4:4 - A component digital video format for high-end studio recordings, where Y, Cb, and Cr are sampled equally.

480i - 480 lines of interlaced video (240 lines per field). Usually refers to 720 x 480 (or 704 x 480) resolution.

480p - 480 lines of progressive video (480 lines per frame). 480p60 refers to 60 frames per second; 480p30 refers to 30 frames per second; and 480p24 refers to 24 frames per second (film source). Usually refers to 720 x 480 (or 704 x 480) resolution.

4C - The four-company entity: IBM, Intel, Matsushita, Toshiba.

525/60 - The scanning system of 525 lines per frame and 60 interlaced fields (30 frames) per second. Used by the NTSC television standard.

5C - The five-company entity: IBM, Intel, Matsushita, Toshiba, Sony.

625/50 - The scanning system of 625 lines per frame and 50 interlaced fields (25 frames) per second. Used by PAL and SECAM television standards.

720p - 720 lines of progressive video (720 lines per frame). Higher definition than standard DVD (480i or 480p). 720p60 refers to 60 frames per second; 720p30 refers to 30 frames per second; and 720p24 refers to 24 frames per second (film source). Usually refers to 1280 x 720 resolution in 1.78 aspect ratio.

8/16 modulation - The form of modulation block code used by DVD to store channel data on the disc. See modulation.

AAC - Advanced audio coder. An audio-encoding standard for MPEG-2 that is not backward-compatible with MPEG-1 audio.

AC - Alternating current. An electric current that regularly reverses direction. Adopted as a video term for a signal of non-zero frequency. Compare to DC.

AC-3 - The former name of the Dolby Digital audio-coding system, which is still technically referred to as AC-3 in standards documents. AC-3 is the successor to Dolby’s AC-1 and AC-2 audio coding techniques.

access time - The time it takes for a drive to access a data track and begin transferring data. In an optical jukebox, the time it takes to locate a specific disk, insert it in an optical drive, and begin transferring data to the host system.

ActiveMovie - The former name for Microsoft’s DirectShow technology.

ADPCM - Adaptive differential pulse code modulation. A compression technique which encodes the difference between one sample and the next. Variations are lossy and lossless.

AES - Audio Engineering Society.

AES/EBU - A digital audio signal transmission standard for professional use, defined by the Audio Engineering Society and the European Broadcasting Union. S/P DIF is the consumer adaptation of this standard.

AGC - Automatic gain control. A circuit designed to boost the amplitude of a signal to provide adequate levels for recording. Also see Macrovision.

aliasing - A distortion (artifact) in the reproduction of digital audio or video that results when the signal frequency is more than twice the sampling frequency. The resolution is insufficient to distinguish between alternate reconstructions of the waveform, thus admitting additional noise that was not present in the original signal.

AMGM_VOBS - Video Object Set for Audio Manager Menu.

analog - A signal of (theoretically) infinitely variable levels. Compare to digital.

angle - In DVD-Video, a specific view of a scene, usually recorded from a certain camera angle. Different angles can be chosen while viewing the scene.

ANSI - American National Standards Institute. (See Appendix C.)

AOTT_AOBS - Audio Object Set for Audio Only Title.

apocryphal - Of questionable authorship or authenticity. Erroneous or fictitious. The author of DVD Demystified is fond of saying that the oft-cited 133-minute limit of DVD-Video is apocryphal.

application format - A specification for storing information in a particular way to enable a particular use.

artifact - An unnatural effect not present in the original video or audio, produced by an external agent or action. Artifacts can be caused by many factors, including digital compression, film-to-video transfer, transmission errors, data readout errors, electrical interference, analog signal noise, and analog signal crosstalk. Most artifacts attributed to the digital compression of DVD are in fact from other sources. Digital compression artifacts will always occur in the same place and in the same way. Possible MPEG artifacts are mosquitoes, blocking, and video noise.

aspect ratio - The width-to-height ratio of an image. A 4:3 aspect ratio means the horizontal size is a third again wider than the vertical size. Standard television ratio is 4:3 (or 1.33:1). Widescreen DVD and HTDV aspect ratio is 16:9 (or 1.78:1). Common film aspect ratios are 1.85:1 and 2.35:1. Aspect ratios normalized to a height of 1 are often abbreviated by leaving off the :1.

ASV (Audio Still Video) - A still picture on a DVD-Audio disc.

ASVOBS - Audio Still Video Object Set.

ATAPI - Advanced Technology Attachment (ATA) Packet Interface. An interface between a computer and its internal peripherals such as DVD-ROM drives. ATAPI provides the command set for controlling devices connected via an IDE interface. ATAPI is part of the Enhanced IDE (E-IDE) interface, also known as ATA-2. ATAPI was extended for use in DVD-ROM drives by the SFF 8090 specification.

ATSC - Advanced Television Systems Committee. In 1978, the Federal Communications Commission (FCC) empaneled the Advisory Committee on Advanced Television Service (ACATS) as an investigatory and advisory committee to develop information that would assist the FCC in establishing an advanced broadcast television (ATV) standard for the United States. This committee created a subcommittee, the ATSC, to explore the need for and to coordinate development of the documentation of Advanced Television Systems. In 1993, the ATSC recommended that efforts be limited to a digital television system (DTV), and in September 1995 issued its recommendation for a Digital Television System standard, which was approved with the exclusion of compression format constraints (picture resolution, frame rate, and frame sequence).

ATV - Advanced television. TV with significantly better video and audio than standard TV. Sometimes used interchangeably with HDTV, but more accurately encompasses any improved television system, including those beyond HDTV. Also sometimes used interchangeably with the final recommended standard of the ATSC, which is more correctly called DTV.

authoring - For DVD-Video, authoring refers to the process of designing, creating, collecting, formatting, and encoding material. For DVD-ROM, authoring usually refers to using a specialized program to produce multimedia software.

autoplay (or automatic playback) - A feature of DVD players which automatically begins playback of a disc if so encoded.

B picture (or B frame) - One of three picture types used in MPEG video. B pictures are bidirectionally predicted, based on both previous and following pictures. B pictures usually use the least number of bits. B pictures do not propagate coding errors since they are not used as a reference by other pictures.

bandwidth - Strictly speaking, the range of frequencies (or the difference between the highest and the lowest frequency) carried by a circuit or signal. Loosely speaking, the amount of information carried in a signal. Technically, bandwidth does not apply to digital information; the term data rate is more accurate.

BCA - Burst cutting area. A circular section near the center of a DVD disc where ID codes and manufacturing information can be inscribed in bar-code format. (See Figure 4.4.)

birefringence - An optical phenomenon where light is transmitted at slightly different speeds depending on the angle of incidence. Also light scattering due to different refractions created by impurities, defects, or stresses within the media substrate.

bit rate - The volume of data measured in bits over time. Equivalent to data rate.

bit - A binary digit. The smallest representation of digital data: zero/one, off/on, no/yes. Eight bits make one byte.

bitmap - An image made of a two-dimensional grid of pixels. Each frame of digital video can be considered a bitmap, although some color information is usually shared by more than one pixel.

bits per pixel - The number of bits used to represent the color or intensity of each pixel in a bitmap. One bit allows only two values (black and white), two bits allows four values, and so on. Also called color depth or bit depth.

bitstream recorder - A device capable of recording a stream of digital data but not necessarily able to process the data.

bitstream - Digital data, usually encoded, designed to be processed sequentially and continuously.

BLER - Block error rate. A measure of the average number of raw channel errors when reading or writing a disc.

block - In video encoding, an 8 x 8 matrix of pixels or DCT values representing a small chunk of luma or chroma. In DVD MPEG-2 video, a macroblock is made up of 6 blocks: 4 luma and 2 chroma.

blocking - A term referring to the occasional blocky appearance of compressed video (an artifact). Caused when the compression ratio is high enough that the averaging of pixels in 8 x 8 blocks becomes visible.

Blue Book - The document that specifies the CD Extra interactive music CD format (see also Enhanced CD). The original CDV specification was also in a blue book.

Book A - The document specifying the DVD physical format (DVD-ROM). Finalized in August 1996.

Book B - The document specifying the DVD-Video format. Mostly finalized in August 1996.

Book C - The document specifying the DVD-Audio format.

Book D - The document specifying the DVD record-once format (DVD-R). Finalized in August 1997.

Book E - The document specifying the rewritable DVD format (DVD-RAM). Finalized in August 1997.

bps - Bits per second. A unit of data rate.

brightness - Defined by the CIE as the attribute of a visual sensation according to which area appears to emit more or less light. Loosely, the intensity of an image or pixel, independent of color; that is, its value along the axis from black to white.

buffer - Temporary storage space in the memory of a device. Helps smooth data flow.

burst - A short segment of the color subcarrier in a composite signal, inserted to help the composite video decoder regenerate the color subcarrier.

B-Y, R-Y - The general term for 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. (See Chapter 3.)

byte - A unit of data or data storage space consisting of eight bits, commonly representing a single character. Digital data storage is usually measured in bytes, kilobytes, megabytes, and so on.