UDF filename used for audio directory
on disc volume
Location within a bitstream that serves as a random
access point. Most common are MPEG I-frames.
DVD Read only specification
DVD Video specification. Organized into Physical,
Logical, and Application sections. v0.9 Draft in April 1996.
DVD Audio specification. Draft expected in Summer
DVD Write once specification
DVD Rewritable specification
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.
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.
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,
Red Book forms the low-level basis for all other
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.
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.
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.
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
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.
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.
area of disc used for coded information. Other areas
of the disc are reserved for lead-in, lead-out,
clamping, and labels.
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
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.
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.
32-bit (4 byte) CRC-like code appended at the end
of the data sector.
enhanced ISO 9660 with multisession.
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.
block code deriviative of the EFM
also know as EFM+, contributed from the
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
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.
Parity bytes concatenated to each interleaved sector.
See Reed-Soloman for specific description.
a multiple of logical blocks (2048 byte sectors).
Means of identifying files and their sector number
Since the 4-byte ID field is super-critical, 2 special
correction bytes (IEC) are added to each sector header.
32-bit field identifying the sector number within
the disc volume.
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.
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
In a dual layer disc, this is the deeper of the
unused physical area at the start of the continuous
unused physical area at the end of the continuous
Coded audio representation which does not employ
compression. Each sample is discretely coded.
user data portion of each sector. 2048 bytes.
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).
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.
the ability to update the disc's table of contents
file for CD-ROM.
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
(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.
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.
Width of the disc. Obviously, this is 12 cm for
"normal" CDs, and 8 cm for small CDs.
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.
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.
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.
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).
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.
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.
Defines the ideal behaviour of a DVD (compliant)
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.
Low-level aspects for DVD specifying the layout
of pits all the way up to the the user bitstream layer.
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.
Arc length of pit along the direction of the track.
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.
Provides information about the timing and presentation
(aspect ratio, angle, etc.) of a program.
information, such as video or audio samples, which
are presented at a specified time.
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.
Two pass (row x col) application of RS
code designed to exploit interleaving of data sectors.
6 bytes in the header of each DVD sector reserved
for future use.
means of exploiting contiguous samples with same
logical collection of bytes at the data layer (after
de-interleaving). At the physical layer, a sector consists of 38688
header field providing the sector number.
a number that inquely identifies the physical sector
on a disc.
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.
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 ))
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.
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
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.
The highest layer of a program. Usually a whole
movie, or television episode. Several titles can be present on a
Distance along radial vector between adjacent tracks.
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).
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.
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.
There are three easily confused definitions of VBR,
each however is viable depending on which layer it is being measured
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.
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.
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
Top level menu linking multiple tiles from a common
Points to the various titles that comprise the disc
volume and identifies disc side and content type.
Note: VMGI is distinct from VMI
Usually a group of pictures.
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.
Describes the nature of the VTS.
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.
Identifies disc side and content type.
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.
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.