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.
packetized 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 color encoding. Various version of PAL use different scanning systems and color 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 color 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 colors that identifies a subset from a larger range of colors. The small number of colors in the palette allows fewer bits to be used for each pixel. Also called a color 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 stop - A function of DVD-Video where a code indicates that video playback should stop and a still picture be displayed.
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.
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 - The depressed area of an optical disc.
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.
pit - A microscopic depression in the recording layer of a disc. Pits are usually 1/4 of the laser wavelength so as to cause cancellation of the beam by diffraction.
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 color depth.
pixel - The smallest picture element of an image (one sample of each color 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 color depth (the number of bits required to represent each pixel).
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.
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. See Chapter 3 for more information.
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. |
