Glossary of DVD Terminology "O to R"

OEM - Original Equipment Manufacturer. Computer maker.

Operating System - The primary software in a computer, containing general instructions for managing applications, communications, input/output, memory and other low-level tasks. DOS, Windows, Mac OS, and UNIX are examples of operating systems.

opposite path - See OTP.

OS - Operating system.

OSTA - Optical Storage Technology Association.

OTP - Opposite track path. A variation of DVD dual-layer disc layout where readout begins at the centre of the disc on the first layer, travels to the outer edge of the disc, then switches to the second layer and travels back toward the centre. Designed for long, continuous-play programs. Also called RSDL. Contrast with PTP.

out of band - In a place not normally accessible.

overscan - The area at the edges of a television tube that is covered to hide possible video distortion. Overscan typically covers about 4 or 5 percent at the edges of the picture but can cover as much as 10 percent.

P picture (or P frame) - In MPEG video, a "predicted" picture based on difference from previous pictures. P pictures (along with I pictures) provide a reference for following P pictures or B pictures.

pack - A group of MPEG packets in a DVD-Video program stream. Each DVD sector (2048 bytes) contains one pack.

packet - A low-level unit of DVD-Video (MPEG) data storage containing contiguous bytes of data belonging to a single elementary stream such as video, audio, control, and so forth. Packets are grouped into packs.

packetised elementary stream (PES) - The low-level stream of MPEG packets containing an elementary stream, such as audio or video.

PAL - Phase Alternate Line. A video standard used in Europe and other parts of the world for composite colour encoding. Various version of PAL use different scanning systems and colour subcarrier frequencies (identified with letters B, D, G, H, I, M, and N), the most common being 625 lines at 50 fields per second, with a colour subcarrier of 4.43 MHz. PAL is also said to mean “picture always lousy” or “perfect at last,” depending on which side of the ocean the speaker comes from.

palette - A table of colours that identifies a subset from a larger range of colours. The small number of colours in the palette allows fewer bits to be used for each pixel. Also called a colour look-up table (CLUT).

pan & scan - The technique of reframing a picture to conform to a different aspect ratio by cropping parts of the picture. DVD-Video players can automatically create a 4:3 pan & scan version from widescreen video by using a horizontal offset encoded with the video.

parallel path - See PTP.

parental management - An optional feature of DVD-Video that prohibits programs from being viewed or substitutes different scenes within a program depending on the parental level set in the player. Parental control requires that parental levels and additional material (if necessary) be encoded on the disc.

part of title - In DVD-Video, a division of a title representing a scene. Also called a chapter. Parts of titles are numbered 1 to 99.

PCI - Presentation control information. A DVD-Video data stream containing details of the timing and presentation of a program (aspect ratio, angle change, menu highlight and selection information, and so on). PCI and DSI together make up an overhead of about 1 Mbps.

PCM - An uncompressed, digitally coded representation of an analog signal. The waveform is sampled at regular intervals and a series of pulses in coded form (usually quantized) are generated to represent the amplitude.

PC-TV - The merger of television and computers. A personal computer capable of displaying video as a television.

pel - See pixel.

perceived resolution - The apparent resolution of a display from the observer’s point of view, based on viewing distance, viewing conditions, and physical resolution of the display.

perceptual coding - Lossy compression techniques based on the study of human perception. Perceptual coding systems identify and remove information that is least likely to be missed by the average human observer.

PES (packetized elementary stream) - A single video or audio stream in MPEG format.

PGCI - Program chain information. Data describing a chain of cells (grouped into programs) and their sector locations, thus composing a sequential program. PGCI data is contained in the PCI stream.

phase-change - A technology for rewritable optical discs using a physical effect in which a laser beam heats a recording material to reversibly change an area from an amorphous state to a crystalline state, or vice versa. Continuous heat just above the melting point creates the crystalline state (an erasure), while high heat followed by rapid cooling creates the amorphous state (a mark). (Other recording technologies include dye-sublimation and magneto-optical.)

physical format - The low-level characteristics of the DVD-ROM and DVD-Video standards, including pits on the disc, location of data, and organization of data according to physical position.

Picture - In video terms, a single still image or a sequence of moving images. Picture generally refers to a frame, but for interlaced frames may refer instead to a field of the frame. In a more general sense, picture refers to the entire image shown on a video display.

Picture stop - A function of DVD-Video where a code indicates that video playback should stop and a still picture be displayed.

PIP - Picture in picture. A feature of some televisions that shows another channel or video source in a small window superimposed in a corner of the screen.

Pit - A microscopic depression in the recording layer of an optical disc. Pits are usually 1/4 of the laser wavelength so as to cause cancellation of the beam by diffraction.

Pit art - A pattern of pits to be stamped onto a disc to provide visual art rather than data. A cheaper alternative to a printed label.

Pixel - The smallest picture element of an image (one sample of each colour component). A single dot of the array of dots that makes up a picture. Sometimes abbreviated to pel. The resolution of a digital display is typically specified in terms of pixels (width by height) and colour depth (the number of bits required to represent each pixel).

Pixel aspect ratio - The ratio of width to height of a single pixel. Often means sample pitch aspect ratio (when referring to sampled digital video). Pixel aspect ratio for a given raster can be calculated as y/x x w/h (where x and y are the raster horizontal pixel count and vertical pixel count, and w and h are the display aspect ratio width and height). Pixel aspect ratios are also confusingly calculated as x/y x w/h, giving a height-to-width ratio. (See Table 4.17.)

Pixel depth - See colour depth.

PMMA - Polymethylmethacrylate. A clear acrylic compound used in laserdiscs and as an intermediary in the surface transfer process (STP) for dual-layer DVDs. PMMA is also sometimes used for DVD substrates.

POP - Picture outside picture. A feature of some widescreen displays that uses the unused area around a 4:3 picture to show additional pictures.

Pre-mastering or premastering - The process of preparing data in the final format to create a DVD disc image for mastering. Includes creating DVD control and navigation data, multiplexing data streams together, generating error-correction codes, and performing channel modulation. Often includes the process of encoding video, audio, and subpictures.

presentation data - DVD-Video information such as video, menus, and audio which is presented to the viewer. (See PCI.)

profile - In MPEG-2, profiles specify syntax and processes such as picture types, scalability, and extensions. Compare to level.

program chain - In DVD-Video, a collection of programs, or groups of cells, linked together to create a sequential presentation.

program - In a general sense, a sequence of audio or video. In a technical sense for DVD-Video, a group of cells within a program chain (PGC).

Progressive scan - A video scanning system that displays all lines of a frame in one pass. Contrast with interlaced scan.

Psychoacoustic - See perceptual encoding.

PTP - Parallel track path. A variation of DVD dual-layer disc layout where readout begins at the center of the disc for both layers. Designed for separate programs (such as a widescreen and a pan & scan version on the same disc side) or programs with a variation on the second layer. Also most efficient for DVD-ROM random-access application. Contrast with OTP.

PUH - Pickup head. The assembly of optics and electronics that reads data from a disc.

QCIF - Quarter common intermediate format. Video resolution of 176 x 144.

Quantise - To convert a value or range of values into a smaller value or smaller range by integer division. Quantised values are converted back (by multiplying) to a value which is close to the original but may not be exactly the same. Quantisation is a primary technique of lossless encoding.

Quantisation levels - The predetermined levels at which an analog signal can be sampled as determined by the resolution of the analog-to-digital converter (in bits per sample); or the number of bits stored for the sampled signal.

QuickTime - A digital video software standard developed by Apple Computer for Macintosh (Mac OS) and Windows operating systems. QuickTime is used to support audio and video from a DVD.

QXGA - A video graphics resolution of 2048 x 1536.

RAM - Random-access memory. Generally refers to solid-state chips. In the case of DVD-RAM, the term was borrowed to indicate ability to read and write at any point on the disc.

RAMbo drive - A DVD-RAM drive capable of reading and writing CD-R and CD-RW media. (A play on the word “combo.”)

Random Access - The ability to jump to a point on a storage medium.

Raster - The pattern of parallel horizontal scan lines that makes up a video picture.

read-modify-write - An operation used in writing to DVD-RAM discs. Because data can be written by the host computer in blocks as small as 2 KB, but the DVD format uses ECC blocks of 32 KB, an entire ECC block is read from the data buffer or disc, modified to include the new data and new ECC data, then written back to the data buffer and disc.

Reed-Solomon - An error-correction encoding system that cycles data multiple times through a mathematical transformation in order to increase the effectiveness of the error correction, especially for burst errors (errors concentrated closely together, as from a scratch or physical defect). DVD uses rows and columns of Reed-Solomon encoding in a two-dimensional lattice, called Reed-Solomon product code (RS-PC).

reference picture (or reference frame) - An encoded frame that is used as a reference point from which to build dependent frames. In MPEG-2, I pictures and P pictures are used as references.

reference player - A DVD player that defines the ideal behaviour as specified by the DVD-Video standard.

regional code - A code identifying one of the world regions for restricting DVD-Video playback. See Table A.21.

regional management - A mandatory feature of DVD-Video to restrict the playback of a disc to a specific geographical region. Each player and DVD-ROM drive includes a single regional code, and each disc side can specify in which regions it is allowed to be played. Regional coding is optional—a disc without regional codes will play in all players in all regions.

Replication - 1) The reproduction of media such as optical discs by stamping (contrast with duplication); 2) a process used to increase the size of an image by repeating pixels (to increase the horizontal size) and/or lines (to increase the vertical size) or to increase the display rate of a video stream by repeating frames. For example, a 360 x 240 pixel image can be displayed at 720 x 480 size by duplicating each pixel on each line and then duplicating each line. In this case the resulting image contains blocks of four identical pixels. Obviously, image replication can cause blockiness. A 24-fps video signal can be displayed at 72 fps by repeating each frame three times. Frame replication can cause jerkiness of motion. Contrast with decimation. Also see interpolate.

Resampling - The process of converting between different spatial resolutions or different temporal resolutions. This may be based on simple sampling of the source information at higher or lower resolution or may include interpolation to correct for differences in pixel aspect ratios or to adjust for differences in display rates.

Resolution - 1) A measurement of relative detail of a digital display, typically given in pixels of width and height; 2) the ability of an imaging system to make clearly distinguishable or resolvable the details of an image. This includes spatial resolution (the clarity of a single image), temporal resolution (the clarity of a moving image or moving object), and perceived resolution (the apparent resolution of a display from the observer’s point of view). Analog video is often measured as a number of lines of horizontal resolution over the number of scan lines. Digital video is typically measured as a number of horizontal pixels by vertical pixels. Film is typically measured as a number of line pairs per millimetre; 3) the relative detail of any signal, such as an audio or video signal. Also see lines of horizontal resolution.

RGB - Video information in the form of red, green, and blue tristimulus values. The combination of three values representing the intensity of each of the three colours can represent the entire range of visible light.

ROM - Read-only memory.

rpm - Revolutions per minute. A measure of rotational speed.

RS - Reed-Solomon. An error-correction encoding system that cycles data multiple times through a mathematical transformation in order to increase the effectiveness of the error correction. DVD uses rows and columns of Reed-Solomon encoding in a two-dimensional lattice, called Reed-Solomon product code (RS-PC).

RS-CIRC - See CIRC.

RSDL - Reverse-spiral dual-layer. See OTP.

RS-PC - Reed-Solomon product code. An error-correction encoding system used by DVD employing rows and columns of Reed-Solomon encoding to increase error-correction effectiveness.

R-Y, B-Y - The general term for colour-difference video signals carrying red and blue colour information, where the brightness (Y) has been subtracted from the red and blue RGB signals to create R-Y and B-Y colour-difference signals.