Glossary

Audio_TS:

UDF filename used for audio directory on disc volume

Anchor Point:

Location within a bitstream that serves as a random access point. Most common are MPEG I-frames.

Book A:

DVD Read only specification

Book B:

DVD Video specification. Organized into Physical, Logical, and Application sections. v0.9 Draft in April 1996.

Book C:

DVD Audio specification. Draft expected in Summer 1996.

Book D:

DVD Write once specification

Book E:

DVD Rewritable specification

Book, Green:

Starting in 1987, with many updates since, Philip's Compact Disc Interactive (CD-I) specification is built upon CD-ROM XA. Introduces features neccessary for interactivity such as a basic operating system, character sets, special effects. Similar to Navigation system in DVD.

Book, Orange:

Starting in 1990. Three parts defines physical aspects of 1. magneto optical erasable 2. write once, and 3. phase change erasable discs. Adds multisession on to CD-ROM XA.

Book, Red:

Circa 1982, this is the original CD-Audio book, also described by the IEC 908 standard. Here, each frame contains 588 channel bits which ultimately reduce to a payload of only 192 audio user bits. The mapping consists of 24 bits of sync, subcode byte coded as a 14 bit EFM symbol, 336 bits of EFM coded user data, 112 bits of error correction bits, and 102 bits of EFM merge bits.

CDs come in two sprial lengths: 63 minutes and 74 minutes. The 74 minute "inner sprial" CD holds 747 MB worth of audio data. That is, 44.1 kHz * 2 channels (Left,Right) * 16 bits/sample * 1/8 bytes/bit * 1/(2^20 bytes/MB) = 747 MBytes.

Each bit of the frame's subcode forms one of the eight subcode channels labled by the letters P, Q, R, S, T, U, V, and W. With 98 frames per sector * 75 sectors per second, the total subcode bytes per disc can total 32 MB. Channels P and Q are used as side information to identify tracks, program, and timing information. Channels R through W were reserved in anticipation of graphics, lyrics, etc.

Red Book forms the low-level basis for all other CD Books.

Book, Yellow:

Circa 1984, the first CD-ROM standard ratified by ISO/IEC 10149. Here 98 Red Book audio frames (each with 24 bytes of payload) form a single 2352 byte sector. The overhead (12 header bytes, 4 sync bytes, and 276 bytes for additonal error correction code) leaves 2048 bytes for payload in Mode 1. Mode 2 skips the extra error correction bytes, increasing the payload to 2324 bytes per sector. A scrambling stage is added to reduce DC energy beyond that provided by the 8/14 channel code.

An extension to Yellow Book called CD-ROM XA (Circa 1989) added ISO 9660 file structure, ADPCM audio channels interleaved onto the same track with the data channel, and still image support.

Mode 2 CD's may have up to 742 Mbytes, which corresponds to a 74 minute Red Book CD. Mode 1 may hold up to 650 MBytes. Mode 1 is used almost exclusively for CD-ROM. Many CD's do not etch the "inner spiral," and therefore hold only 63 minutes of audio or 550 MB of Mode 1 payload.

Book, White:

Circa 1993, known as "Video CD" and "Karaoke." Built upon the CD-ROM XA file structure featuring a file payload of SIF-rate MPEG-1 Video (ISO/IEC 11172-2) and MPEG-1 Layer II Audio (ISO/IEC 11172-3) streams multipliexed in regular packets the size of sectors via MPEG-1 Systems (ISO/IEC 11172-1). The video sample rate is limited to 352x240x30 frames/sec or 352x288x25 Hz, and a coded bit rate of 1.15 Mbit/sec for video and 224 kbit/sec for Layer II stereo audio.

White Book should not be confused with defunct CD Video, a 1987 format which essentially is a smaller (12 cm) version of today's analog composite video (30 cm) laserdisc. A typical disc would hold 20 minutes of digital audio plus 5 minutes of music video.

Book, Blue:

CD Plus or "Enhanced CD" supporting two session (Audio and Data) encoded onto the same disc. Still pictures and data files based upon CD-ROM XA.

Cross Interleaved Reed-Soloman code (CIRC):

Reed-Soloman method using a small interleave window over a frame of audio: 24 bytes (much smaller than DVD's 2-D product code over 2048 bytes--- 32 Kbytes when considering sector interleave).

Clamping_Area:

area of disc used by CD player to grip and spin the disc. Force from the motor is transfered to the disc here. At the inner most radius of disc.

Constant bit rate (CBR):

Attribute of bitstream where the number of bits delivered to the MPEG System buffer (STD) and/or Video Buffer Verifier ( VBV) is constant within when measured over each picture period.

Data recorded area:

area of disc used for coded information. Other areas of the disc are reserved for lead-in, lead-out, clamping, and labels.

Digital Versitale Disc:

Generic name for a family of related disc formats encompasing Video, Audio, and computer file storage (CD-ROM). 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... with respect to the player.

Currently, no Book has been defined for Photo CD.

Data Search Information (DSI):

Along with PGCI, these packets are part of the 1.00 mbit/sec overhead in video applications (Book B). They are removed before entering the MPEG systems buffer, a.k.a. System Target Buffer (STD). These packets contain navigation information which makes possible to search and maintain seamless playback of the Video Object Unit (VOBU). The most imporant 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.

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.

Error Detection Code (EDC):

32-bit (4 byte) CRC-like code appended at the end of the data sector.

ISO 13490:

enhanced ISO 9660 with multisession.

ECC Constraint Length:

the number of sectors that are interleaved to combat bursty error characteristics of discs. 16 sectors are interleaved in DVD. In other applications such as Direct Broadcast Satellite, the popular interleave length is 12 (?) sectors, each of which are only 188 bytes long instead of DVD's 2048 bytes.

Interleaving takes advantage of typical localaized disc defects such as scratch marks by spreading the error over a larger data area, thereby increasing the chance that the error correction codes can conceal the error.

8/16 Modulation:

block code deriviative of the EFM also know as EFM+, contributed from the Sony-Philips camp.

EFM:

This low-level and very critical channel coding technique maximizes pit sizes on the disc by reducing frequent transitions from 0 to 1 or 1 to 0. CD employs pulse width modulation, representing 1's as Land-pit transititions along the track. The 8/14 code maps 8 user data bits into 14 channel bits. In the 1982 compact disc standard (IEC 908 standard), 3 merge bits are added to the 14 bit block to further eliminate 1-0 or 0-1 transitions between adjacent 8/14 blocks.

EFM Plus:

DVD's EFM+ method is a derivative of EFM. It folds the merge bits into the main 8/16 table. EFM+ may be covered by U.S. Patent 5,206,646.

Error Correction Code:

Parity bytes concatenated to each interleaved sector. See Reed-Soloman for specific description.

File:

a multiple of logical blocks (2048 byte sectors).

File system:

Means of identifying files and their sector number on disc.

ID Error Correction (IEC):

Since the 4-byte ID field is super-critical, 2 special correction bytes (IEC) are added to each sector header.

Identification Data (ID):

32-bit field identifying the sector number within the disc volume.

ISO 9660/High Sierra:

Orignally known as "High Sierra," this international standard specifies 3 levels of CD-ROM logical files. The first level is the same as MS-DOS (8 characters plus 3 extension), the second level allows 30 character long filenames.

Layer 0:

In a dual layer disc, this is the layer closest to the optical pickup beam and surface of the disc. Dual layer discs are 10% less dense than single layer discs due to crosstalk between the layers.

Layer 1:

In a dual layer disc, this is the deeper of the two layers.

Lead-in:

unused physical area at the start of the continuous track spiral.

Lead-out:

unused physical area at the end of the continuous track spiral.

Linear PCM:

Coded audio representation which does not employ compression. Each sample is discretely coded.

Main data:

user data portion of each sector. 2048 bytes.

Middle area:

unused physical area that marks the transition from layer 0 to layer 1. Middle Area only exists in dual layer discs where the tracks of each layer are in opposite directions (movie applications).

Moving Pictures Experts Group (MPEG):

international standards committee created by Leonardo Chiariglione in 1988 with purpose of defining a means to digitally code video and audio on compact discs. Later, the MPEG-2 project expanded the scope to include HDTV and SDTV rate programs over many mediums (disc, broadcast, tape). The language of MPEG (syntax) defines the structure of the bitstream. The semantics of MPEG define a decoder which reconstructs bitstreams via a pre-defined rule base (algorithms) into frames of video and audio samples.

multisession:

the ability to update the disc's table of contents file for CD-ROM.

mux_rate:

defined by ISO/IEC 13818-1 as the combined rate of all elementary streams (video and audio) packets common to one program, including systems packet overhead (headers, stuffing). This rate also includes the VBI and subpicture private stream data (they are treated as private stream type as far as MPEG is concerned). Always specified as 10.08 mbit/sec since this is the rate at which user data arrives into the track buffer.

Numerical Aperture (NA):

(optical science). The numerical aperture is a unitless measure of the light gathering capacity of the lens system and determines its resolving power and depth of field. It is computed as the sine of one-half the angular aperture (collection angle) times the refractive index of the lens medium. A vacuum has NA of 1.0 by definition. The higher the number, the better.

Opposite track:

Dual layer disc where layer 0 and layer 1 have opposite track directions. Layer 0 reads from the inside to outside of disc, whereas Layer 1 reads from the outside to the inside. The disc always spins clockwise, regardless of track structure or layers. This mode facilitates movie playback by allowing seamless transition from one layer to another. In computer application (CD-ROM), it usually makes more sense to use the Parallel Track format where random access time is more important.

Outer diamater:

Width of the disc. Obviously, this is 12 cm for "normal" CDs, and 8 cm for small CDs.

Pack:

collection of MPEG systems stream packets. In White book and DVD, one pack is coded per sector. This is a subset of the general case where more than 1 packet usually comprises a Pack()... at least that was the intent of the MPEG systems specification.

Packet:

In DVD, each packet consists of 2048 byte from one stream (1 of up to 8 audio streams, 1 video, 1 private VBI stream, etc.) aligned to a DVD sector. Some bytes of the packet are consumed by the MPEG-2 Systems Program stream header.

PAL/NTSC:

Technically speaking, DVD players have nothing to do with either PAL or NTSC, since these formats are composite broadcast signals. Nit-picky television engineers will issue you a citation for using "PAL" and "NTSC" too loosly, but there really isn't a more convenient way of describing one of two fundamental video formats in the world. MPEG bitstreams represent component video signals only. Even though DVD is strictly a component format, players may output component analog video (via 4-pin S-video jack) at line rates and frame rates nearly equivalent to PAL and NTSC signals. Composite signal output (RCA jack) is the least common denominator.

Parallel track:

Dual layer disc where layer 0 and layer 1 have the same clockwise (as seen from the readout side of the disc) spiral direction (inside radius to outside radius).

Part of tile:

Subset of a Title. Useful for designating a collection of video objects which belong to a common scene. Analgous to "Chapters" on analog video laserdisc.

Player:

Embodiement of a DVD decoder system which executes the Navigation system and performs all decoding from the channel layer at least up to the track buffer layer. In future, external MPEG decoders may perform the actual video and audio reconstruction, but copyright issues currently prevent this.

Player Reference Model:

Defines the ideal behaviour of a DVD (compliant) Player.

Photo CD:

Kodak's Photo CD for representing 24-bit 4:2:0 YCbCr images hierarchically at resolutions of up to 3072x2048 pixels. Thumbnails image representation is also part of the Photo CD spec. Built upon CD-ROM XA.

Physical format:

Low-level aspects for DVD specifying the layout of pits all the way up to the the user bitstream layer.

Pit:

A thin depression on disc, usually deep as 1/4 of the reference beam's wavelength. A pit is designed to cause cancelation of the beam at that point along the track.

Pit length:

Arc length of pit along the direction of the track.

Program Chain Information (PGCI):

In pointer fashion, describes the physical sector locations of each program comprising the program chain. Sector addresses for non-seamless angle changes (user selected branch) and subpicture highlight control are included in the PCI packet. PCI is part of the 1.00 mbit/sec user data overhead, along with DSI packets, that is removed prior to entering the system target decoder (STD) buffer.

Note: an extra 'G' is added to the abbreviation in order to distinguish from Program Chain Information's abbreviation.

Presentation Control Information (PCI):

Provides information about the timing and presentation (aspect ratio, angle, etc.) of a program.

Presentation Data:

information, such as video or audio samples, which are presented at a specified time.

Reed-Soloman:

Cyclical method of error correction first published in the June 1960 issue of Journal of the Society for Industrial and Applied Mathematics in a paper titled "Polynomial Codes over Certain Finite Fields" by I.S. Reed and G. Solomon.

Reed-Soloman Product Code:

Two pass (row x col) application of RS code designed to exploit interleaving of data sectors.

Reserved bytes:

6 bytes in the header of each DVD sector reserved for future use.

run-length coding:

means of exploiting contiguous samples with same value.

sector:

logical collection of bytes at the data layer (after de-interleaving). At the physical layer, a sector consists of 38688 channel bits.

sector information:

header field providing the sector number.

sector number:

a number that inquely identifies the physical sector on a disc.

sequence:

MPEG definition of a set of coded pictures which are dependently coded. Within a sequence, all pictures adhere to a common bitrate (CBR), buffer size, picture size, aspect ratio, and frame rate.

scanning velocity:

rate at which the laser pickup beam travels along the spiral track. While the scanning velocity is fixed (Constant Linear Velocity or CLV), the angular velocity of the disc is regulated in order to maintain CLV. Consequentially, the rate of revolution varies from approximately 9 Hz (outer spiral) to 24 Hz (inner spiral). revoltion rate = (scanning velocity / (radius * 2 * PI ))

scrambling:

further reduces DC energy of bitstream signal over the reduction already provided by EFM Plus. Scrambling is more of a global reducer of DC values since it spans many more bits than EFM. Performed prior to EFM+ by the Encoder, and after EFM+ by the Player.

sup-picture:

A simple picture intended to be superimposed over the video. Variable in display size, but bounded to CCIR 601 picture dimensions (720x480 for NTSC-rate displays or 720x576 for PAL-rate displays). See this page for more information.

substrate:

Backbone medium of a disc providing rigidity. The polycarbon substrate is transparent. The laser beam passes through the substrate to reflect off the recorded layer. The thickness of the substrate is critical to the optical pickup system. For this reason, the original CD format was never double sided, since this would have doubled it's thickness and introduced a glue layer which was error prone in the early 1980s. Laserdisc (circa 1976) did in fact bond two discs, yielding a total thickness of 2.4 mm.... twice that of CD.

Title:

The highest layer of a program. Usually a whole movie, or television episode. Several titles can be present on a DVD volume.

Track pitch:

Distance along radial vector between adjacent tracks.

Track buffer:

In the player model, this unit is responsible for smoothing flucuations in the user bitstream caused by irregular disc accesses. It also performs any regulation from the 11.08 mbit/sec constant user data rate to a variable rate MPEG stream (mux_rate) ranging anywhere from 1.0 to 10.8 mbit/sec. The mux_rate is always specified as a constant 10.08 mbit/sec, even though the sum of all the multiplexed streams (Video, Audio, Subpicture, VBI) may be much less (and prone to rapid flucuation).

User Data:

All data above the channel layer. This includes Video, Audio, Systems packet overhead, Subpictures, Navigation data, DSI packets, and File Management data. DVD reference data rate is specified as 11.08 mbit/sec.

User interface:

A lowest common demoniator of functions providing interactive selection of disc programming content. Includes: Ten keys and cursor keys, menu graphics and high-light areas, menu still picture with subpicture, and MPEG graphics.

Variable Rate Bitstream (VBR):

There are three easily confused definitions of VBR, each however is viable depending on which layer it is being measured over.

At the lowest layer, a VBR video stream varies over the duration of a sequence.

At the program layer, a program stream consisting of several concatenated sequences, each with different bitrates, is considered a variable rate stream. The bitstreams are sequence-wise constant. This has important implications for the MPEG video decoder, whose buffer (VBV) regulates data flucuations within a smaller time window (cononically around 0.25 seconds).

To the user way at the top, the fact that the bit rate from one program to another may differ radically, would be considered variable bit rate.

Vertical Blanking Interval (VBI):

In analog television, this is the first few scan lines within a field that do not contain picture information. They appear as static at the top of the image. This time period is used by the electron gun to reposition itself from the bottom of the previous field to the top of the current field. (This does not happen instantaneously). All electron gun based displays, including computer, have VBI. Since this period (usually less than 10% of the total video signal time) is not used to convey picture information, it became the natural place to insert side information such as teletext and closed caption bitstreams.

Video Buffer Verifier (VBV):

MPEG concept defined in ISO/IEC 13818-2 (MPEG-2, Annex C) which employs a fixed size buffer to handle the transition of the channel bit rate to the rapidly flucuating coded bit rate of individual MPEG pictures. The scope of the VBV is only within a sequence. The VBV is built upon a framework of several axioms of decoder behavious which are unfortunately not very well described in the spec. These include:

  • display pictures have known durations, but the time to download the corresponding coded bits into the VBV varies. This time is dependent on the bitrate of the delivery and the coded size of the picture being delivered to the VBV. For example, I frames will take an average of 4 picture periods to download, whereas B pictures will take half an average picture period.
  • all coded pictures are not equal in size. Ratios of 15:5:2 are common for I, P, and B pictures respectively.
  • a picture is decoded instantenously in the VBV model, yet a real-world decoder will account for the time it takes to decode a picture by increasing the size of the VBV buffer.
  • a B picture is displayed almost as soon as it is decoded. An I or P picture is not displayed until the next I or P picture is decoded. This is known as the reorder delay.
  • the first vbv_delay of a sequence is arbitrary, but is usually kept large. From there on, subsequent vbv_delay values are directly related to the coded size of a pictures and the interval of the picture being displayed while a picture is being decoded.
  • Video Manager:

    Top level menu linking multiple tiles from a common point.

    Video Manager Information (VMGI):

    Points to the various titles that comprise the disc volume and identifies disc side and content type.

    Note: VMGI is distinct from VMI

    Video Object (VOB):

    Usually a group of pictures.

    Video Tile Set (VTS):

    a maxmium of 10 files (in ISO 9660 structure) may comprise a video tile set. Each video tile set is preceeded by a Management File. Each file in turn is limited to 1 GByte in size.

    Video Tile Set Information (VTSI):

    Describes the nature of the VTS.

    Video_TS:

    UDF filename used for video directory on disc volume. Files under this directory name contain pointers to the sectors on the disc which hold the program streams.

    Volume Management Information:

    Identifies disc side and content type.

    Volume Space:

    collection of sectors that make the volume. Not all sectors on the disc comprise the volume. Some near the inner and out spiral are are used as leader.

    UDF Bridge:

    A "bridge" ties several specifications together. This garbage phrase "bridge disc" was used mostly to describe how CD-I made a bridge to the CD-ROM XA format for its physical and logical layer specification. White book later did the same. "Bridge" is now a general term to denote the linking of one spec to another. In DVD Book B, a bridges are drawn to UDF, MPEG-2, Dolby AC-3, etc.