DVD Glossary
ASPECT RATIO |
BITSTREAM |
DTS |
DOLBY DIGITAL |
LETTERBOX |
16:9
See aspect
ratio.
3-2 pulldown processing
A process which improves the look of film-based video when it is converted
to progressive-scan. The frame rate for film is 24 frames per second (24
fps), and that's the way movies are stored on DVD. The frame rate for
broadcast video in the U.S. is 30 frames
per second (or more precisely, 60 fields
per second).
So, one of the primary tasks of the MPEG decoder inside every DVD
player is to take the 24 fps data stored on the DVD and convert it to
60-fields-per-second video for TV viewing. Since 24 doesn't divide evenly
into 60, a process called "3-2 pulldown" is employed, where 3
video fields are created from the first film frame, then 2 fields from the
next frame, then 3, then 2, 3-2-3-2-3-2, etc. The result is
60-fields-per-second interlaced-scan video, and that's the end of the story
for non-progressive-scan DVD players.
Progressive-scan DVD players add an important additional step to create a
better-looking picture ? they generate a progressive-scan video signal
through a process called de-interlacing (sometimes called
"line-doubling"). The de-interlacer's first task is to look at the
interlaced video signal as it leaves the MPEG decoder and determine whether
its original source was 24-frame-per-second film or 30-frame-per-second
video. The original frame rate determines the type of processing necessary
to create an optimized progressive-scan signal.
Advanced de-interlacers detect 3-2 pulldown on film-based sources and apply
3-2 pulldown processing to create a 60-frame-per-second progressive-scan
signal that maintains the original frame integrity, with no mixing of
non-matching fields. This processing eliminates jagged edges on still
objects and moving angled lines, producing video with the naturally smooth
look of film.
4:3
See aspect
ratio.
Anamorphic
A type of widescreen display format commonly found on DVD movies. It is
optimized for playback on a TV with 16:9 aspect ratio (or TVs with a
"vertical squeeze" viewing mode like Sony's 16:9 Enhanced). On a
standard TV, anamorphic material looks horizontally squeezed. Anamorphic
DVDs are often labeled on their cases "enhanced for 16x9
televisions," "enhanced for widescreen televisions,"
"16x9 anamorphic," or "anamorphic widescreen."
An anamorphic widescreen DVD has significantly higher resolution than a
letterboxed widescreen DVD. For example, for a film shot in the
commonly-used 1.85:1 aspect ratio, a letterboxed DVD presentation uses only
345 vertical scan lines (the remaining scan lines are taken up by the
horizontal black bars above and below the image). That same film in
anamorphic widescreen will use anywhere from 460 to the full 480 scan lines.
See aspect
ratio for more information.
Aspect ratio
The shape of an image or display screen expressed as a width-to-height
ratio. The NTSC analog television standard is the rather square-like 4:3 (1.33:1),
while anamorphic
DVDs and High-definition TV broadcasts are in the wider 16:9 (1.78:1) shape.
Most movies are made for the wide screen of a theater, and are originally
displayed at the wider ratios of 1.85:1 or 2.35:1.
DVD's data storage capacity makes it possible to include multiple
versions of a movie on a single disc. It's not unusual for a DVD disc to
feature a Standard (4:3) version on one side and a Widescreen (16:9) version on the
other.
For TVs with standard 4:3 screens, movies must be
re-formatted to either "letterbox" or "pan-and-scan." If
you usually rent or buy VHS movies, you're probably used to pan-and-scan
versions, which are preceded by this message: "This film has been
modified from its original version. It has been formatted to fit your
screen."
Pan-and-scan provides an image with full height, but shows a central
"window" that is only 75% of the original widescreen width. What
this window shows is determined by the preferences of the person(s)
performing the film-to-disc transfer.
Widescreen DVDs will be either letterboxed or anamorphic. For letterboxed
DVDs, the player uses a "letterbox filter" that adds horizontal
black bars to the top and bottom of the picture. What you see is a short,
rectangular image that maintains the movie's full original width.
Anamorphic DVDs deliver a higher-resolution widescreen presentation. For an
explanation of anamorphic widescreen, see anamorphic.
Bitstream
A signal that contains digital data in its undecoded state. An example is
the signal that's fed through a DVD player's digital output(s) coax or
optical, which
carries Dolby Digital, DTS, or PCM signals.
Chrominance
The color information portion of a video signal that describes an image's
color shade and vividness.
Component video
A video signal in which the brightness (luminance) and color (chrominance)
portions of the signal are processed separately. Component video signals
provide greater color accuracy than S-video or composite signals.
Nearly all new DVD players and many new TVs
include 3-jack component video connections (green, blue, red).
Why is component video superior to
S-video? Where S-video separates the luminance and chrominance portions of
the signal, component video goes a step further and splits the chrominance
portion into two components. The benefits ? improved color accuracy and
less color bleeding ? are especially noticeable on larger-screen TVs.
Composite video
A video signal in which the brightness and color portions of the signal are
combined. Examples of composite video include standard VHS, laserdisc, and
NTSC broadcast TV. A DVD player's standard RCA-type video jack (yellow) provides a
composite video signal.
Copy protection
A system for preventing the unauthorized reproduction of copyrighted media
like movies or music. The DVD format includes both digital and analog forms
of copy protection. You will probably not be able to copy DVDs with your
VCR. (In fact, because the copy protection system is triggered by a circuit
found in most VCRs, simply playing a DVD and running the signal through your
VCR will often result in a distorted picture. You should bypass the VCR
altogether and connect your DVD player directly to your TV.)
De-interlacing
The process of converting an interlaced-scan video signal (where each frame
is split into two sequential fields) to a progressive-scan signal (where
each frame remains whole). De-interlacers are found in progressive-scan DVD
players and digital TVs. More advanced de-interlacers include a feature
called 3-2
pulldown processing. With TVs, de-interlacing is sometimes referred to
as "line-doubling" or "upconversion."
Digital output
All DVD players include at least one digital audio output for sending the
Dolby Digital or DTS bitstream to a compatible decoder (which is usually
built into an A/V receiver). Digital data transfer offers extremely wide
bandwidth, immunity to RF interference, and an easy one-cable connection.
The two most common types of digital output are digital coaxial (round orange or black) and optical (square black).
Although a coaxial digital jack looks like a standard RCA-type audio jack,
both coaxial and optical jacks require special cables to connect to the
digital input of your Dolby Digital/DTS-equipped receiver. Note: Most DVD
players do not include digital audio cables.
Digital-to-analog converter (DAC)
An electronic circuit that converts a series of digital "words"
into a continuous analog signal. DVD players include separate DACs for audio
and video.
Dolby? Digital
A discrete multichannel digital audio standard offering enhanced sonic
realism. Dolby Digital is normally associated with 5.1-channel surround
sound. Though this channel configuration is common, it is only one of
several possible variations ? a "Dolby Digital" soundtrack can
mean anything from 1 to 5.1 channels.
If you are looking for titles with a 5.1 soundtrack, you should
carefully read each DVD disc's packaging. Relatively few older movies with
stereo or mono soundtracks will be remastered with 5.1-channel surround for
DVD.
Dolby Digital 5.1 soundtracks will in most cases provide the most satisfying
sound quality for a home theater system. It is referred to as a 5.1-channel
system because it offers five full-bandwidth channels (including true stereo
surrounds), plus a "low frequency effects" subwoofer channel.
Unless your DVD player has its own built-in Dolby Digital decoder, you'll
need to connect your player to a A/V receiver or processor that can take the
digital bitstream from the disc and convert it into 6 channels of audio.
Dolby Digital uses a data compression technique called "perceptual
coding" to reduce the original amount of audio data by a factor of
about 10:1.
Downmixed audio
If you don't have a Dolby Digital system, you can still enjoy excellent Pro
Logic? or stereo sound. All DVD players have the ability to take a
5.1-channel Dolby Digital soundtrack and "downmix" it to two
channels, which can then be sent to a stereo TV, a stereo receiver, or to an
A/V receiver with Dolby Pro Logic decoding.
DTS? (Digital Theater Systems)
DTS is a multichannel audio format. Like Dolby Digital, DTS is
primarily a 5.1-channel format. The compression scheme used in DTS is far
less "lossy" than Dolby Digital, so
theoretically it should sound better, but few people can tell the difference.
Nearly all new DVD players are DTS-compatible; some DVD players and most new A/V receivers include DTS decoding.
DVD-Audio (DVD-A)
A music-oriented DVD format that can carry up to 6 channels of 96kHz/24-bit
audio (music for 5.1-channel home theater systems), or 2 channels of ultra
high-resolution 192kHz/24-bit audio. Most DVD-Audio discs also carry
lower-resolution Dolby Digital or stereo soundtracks for playback on DVD
players that lack DVD-Audio decoders. A DVD-Audio disc usually also contains
lyrics, menus, and related still images that display on your television.
DVD-R/RW, DVD-RAM, DVD+R/RW
See recordable
DVD.
Field
In interlaced-scan video, each complete frame is split into 2 sequential
fields, each of which contains half the scanning lines of the frame. One
field contains the odd scanning lines, and the other field the even lines.
Frame
A complete, individual picture in a movie film. In a video signal, a frame
contains all of the picture's scanning lines.
Frame rate
The rate at which frames are displayed. The frame rate for movies is 24
frames per second (24 fps). In regular NTSC video, the frame rate is 30 fps.
HDCD? (High Definition Compatible Digital)
An enhanced method of audio recording for CDs developed by Pacific
Microsonics. HDCD claims to be able to capture 20-bit resolution. Although
the HDCD-enhanced information can only be heard using a DVD or CD player
with built-in HDCD decoding, HDCD discs are still playable on regular DVD
and CD players.
Interlaced scan
An interlaced-scan video signal splits each complete picture frame into 2
sequential fields, one containing the frame's odd scanning lines, and the
other containing the even lines. Interlaced scan has been an effective way
to maximize our 60-year-old NTSC video system, but it is prone to problems
like motion artifacts, which become more noticeable on TV screens larger
than 27". These artifacts are generally reduced or eliminated by
progressive-scanning.
Letterboxing
The scaling of a widescreen image to fit a standard 4:3 aspect ratio TV
screen by shrinking the image so that the width fits exactly. The horizontal
black bars that appear above and below the image are actually recorded with
the picture, so some of the picture's vertical resolution is lost when you
view it. Letterboxing is much more common on DVD movies than VHS videos.
Luminance
The brightness component of a color video signal. Determines the level of
picture detail.
Meridian Lossless Packing or MLP is the data-reduction
technique selected for DVD-Audio. MLP sounds better because it is a lossless
data algorithm. It is not like MP3 for instance. You get back exactly
what you put in, so it does not distort or change any of the audio
information. MLP on average reduces the size of the file by about
50%. So, with MLP you can put 6 channels of 24/96 on the disc, and still not
hit the 9.6 Mbs data limitation. MLP can also be used to simply get longer
recording times onto the disc.
MPEG2
The digital video signal compression standard used for DVD. This adaptive,
variable bit-rate process is able to allocate more bits for complex scenes
involving a lot of motion, while minimizing the bits in static scenes. The
average data rate for DVD is 3.5 Mbps (million bits/second).
MPEG stands for Moving Picture Experts Group.
Multi-language capability
DVD is designed to make it easier for movies to be distributed in multiple
languages. A single DVD disc can contain soundtracks in up to 8 different
languages.
In addition to multilingual dialog, a DVD also has space for subtitles in
up to 32 languages. Note: the number of soundtracks and subtitles will vary
from disc to disc depending on the length of the movie and whether or not
other playback features are included.
Pan-and-scan
A technique for making a widescreen movie fit a standard TV's 4:3 aspect
ratio by showing only selected portions of the original image. This is the
standard practice on VHS videos ("formatted to fit your screen"),
but is less common on DVDs.
Parental lockout
A small percentage of DVD movies include variable ratings capability.
According to the movie rating level you select, the player will skip over
certain scenes, playing the version that you choose from those available on
the disc.
PCM (Pulse Code Modulation)
The digital audio signal format used for Compact Discs (CD). Digital outputs on
DVD players are often labeled "Bitstream/PCM" because they can
send the Dolby Digital or DTS bitstream from a DVD, or the PCM bitstream
from a CD.
Perceptual coding
A type of data compression used in recent digital audio and video formats.
Audio examples include Dolby Digital and MP3. The best example of video
compression is MPEG2,
which is used for DVD and digital satellite TV. These forms of data
compression are based on research into how humans perceive sounds
and images.
Perceptual coding omits "imperceptible" sound and image data
which is redundant or which is judged to be masked by similar information.
In the case of DVD, by discarding a lot of redundant and
unnecessary information, it's possible to fit multiple versions of a movie
on a 4.8 inch disc.
Progressive scan
Instead of splitting each video frame into two sequential fields like
interlaced scan, progressive scan displays the entire frame in a single
sweep. So, where a standard DVD player's 480i output displays 30 frames (60
fields) per second, a progressive-scan player's 480p output displays 60 full
frames per second. Progressive-scan picture quality is more like film, with
more fine detail and less flicker. Progressive-scan viewing requires a compatible
digital TV.
Recordable DVD
DVD recorders function like a VCR only using recordable DVDs instead of
videotape.
There are three recordable-DVD types. These three types are DVD-R/RW, DVD-RAM,
and DVD+R/RW. Some of these formats use discs that can only be recorded
once; others use discs that can be erased and re-recorded.
- Write-once: DVD-R, DVD+R
- Rewriteable: DVD-RW, DVD+RW, DVD-RAM
For more details on recordable DVD, DVD
Recorders.
Region codes
The DVD standard includes codes which limit playback to a specified geographical
region of the world.
DVD players have a built-in region code lockout feature, while the DVD discs
may or may not contain a code. A
player will be unable to play a disc that has a different region code. Discs
may contain codes for more than one region, or may not have any code, which
allows them to be played on any player in any country.
Regional
Coding: The DVD
regions are defined as follows:
Region 1 - United
States of America, Canada
Region 2 - Europe,
including France, Greece, Turkey, Egypt, Arabia
and South Africa
Region 3 - Korea, Thailand,
Vietnam, Borneo and Indonesia
Region 4 -
Australia and New Zealand, Mexico, the
Caribbean, and South America
Region 5 -
India, Africa, Russia and former USSR countries
Region 6 - Peoples Republic of China
Resolution
In DVD,
resolution is the number of pixels in the height
and width of the picture frame. DVD resolution
is 720X480.
RF Output
Used on a laserdisc player to
carry the Dolby Digital signal over a coaxial
cable.
RSDL
Reverse Spiral
Dual Layer. A type of DVD that allows twice (8.5
GB) the ordinary amount of DVD data per
side.
S-Video
A cable that
carries the luminance ("Y") and chrominance
("C") on separate channels. Same as
Y/C.
Sampling
Process of
creating a digital representation of an analog
signal. Standard CD PCM is sampled at a rate of
44.1 kHz (44,100 "samples" of the sound are
taken per second).
Signal-to-Noise ratio (video)
This ratio is a measure of the content (desirable) portion of the video signal in
relation to the noise (undesirable) in the signal. As with audio, video signal-to-noise is
measured in decibels (dB). The way the decibel scale works, if component A
has a signal-to-noise (S/N) ratio of 20 dB and component B has a S/N ratio
of 30 dB, component B will have ten times less noise in the signal than
component A.
A S/N ratio describes how "clean" a video signal is. A standard VHS VCR may have a S/N
ratio of 40 dB; a laserdisc player, 50 dB. DVD is rated to
deliver a video S/N ratio of 65 dB.
SPDIF
Sony/Philips Digital Interface. The standard for
transmitting digital data (like Dolby Digital)
on consumer-grade components. Uses either a
75-ohm coaxial or TOSLINK optical cable.
Substrate
The clear
material (polycarbonate) that surrounds and
protects the stamped information on a DVD. The
substrate is thin and helps the DVD ensure
greater accuracy in the laser pick-up, because
the laser is less likely to refract.
Super Audio CD (SACD)
A digital audio format developed by Sony and Philips.
Instead of using PCM audio encoding like CDs, SACDs use Direct
Stream Digital? (DSD) encoding. DSD is a 1-bit technology that samples
music at the rate of 2.82 million times per second, compared to
standard CD's rate of 44,100 times per second. All SACDs contain a
high-resolution stereo mix; many also contain a high-resolution surround
mix, with up to 6 independent channels.
THX
A
specification developed by Lucasfilm Ltd,
designed to indicate that a product meets the
minimum specifications for achieving high
performance, to ensure a high-quality playback
of a film or video. Timbre Matching
Making sure that loudspeakers
in a surround sound setup have equivalent tonal
characteristics. This helps to ensure that sound
is uniform as sound moves between
speakers.
Toslink
A plastic
fiber optic cable used for SPDIF (e.g. DVD
optical output). Variable Bit Rate
The flow of data being processed
on a DVD can be variable, depending on the
complexity of the information being processed.
Fast moving, dynamic scenes require a high data
rate, while a static (non-moving) image requires
a lower data rate.
Widescreen
An
image with an aspect ratio greater than 1.33:1.
Can include aspect ratios: 1.66:1, 1.85:1, and
2.35:1. |
