DVDs are identical to CDs in size and appearance, but advances in
the amount of information in the form of bits and bytes that can be
recorded onto these discs has meant that full length movies can be stored on a DVD - and the picture quality is extremely good.
(see the difference between CD and DVD) They are also, unlike VHS tapes, very
robust, last longer, and there's no messy tape to get snagged up in
video recorders. More... about
DVD-Video was originally designed
to meet the requirements of the movie industry, in particular for a
complete movie on a single 'compact' optical disc. The use of MPEG-2
video compression has been shown to give superlative results, far
better than VHS and better than Laserdisc.
DVD-Video also offers
full surround sound, subtitling, a choice of display formats and
user interaction for non-linear video applications.
DVD-Video players were launched in
Japan in November 1996, in the USA in March 1997 and in Europe in
1998. Since then DVD-Video has grown faster than any other consumer
electronics format in all these regions. Many thousands of titles
and tens of millions of players are now in use around the world,
with annual sales of players and discs almost doubling each year in
some regions. DVD
Video recorders that use recordable DVD discs are also
now available to consumers,
and are rapidly replacing VCRs.
The DVD-Video specification was
written and is now maintained by the DVD Forum working group WG1,
which comprises a number of task groups concerned with both
read-only and recordable disc formats.
DVD-Video is now replacing VHS as
the format of choice for pre-recorded movies, both retail and rental
and disc sales now exceed VHS sales in many regions. With the
introduction of recordable versions DVD-Video is now set to replace
the VHS VCR for home video recording as well as playback of pre-recorded
The Hollywood based Motion Picture
Studio Advisory Committee defined the following requirements for the
- 135 minutes on one side of a
single disc (covering 99% of all movies).
- Video resolution better than
- CD quality surround sound for
true home cinema listening.
- 3 to 5 languages (audio) per
title on one disc
- 4 to 6 subtitles per title on
- Pan-scan, letterbox and
- Parental lock features
- Copy protection
- Compatibility with existing CDs
- Chapter division and access
(like Video CD)
- Manufacturing cost similar to
current CD costs.
The Video CD format
was studied, but was rejected as it could not offer the necessary
combination of quality and playing time, hence the need for a new
higher capacity disc format that has been realized in DVD. The above
requirements have all been met in the DVD-Video specification.
The DVD-Video specification
provides the following features:
- 133 minutes of high quality
MPEG-2 encoded video with multi-channel surround sound audio.
- The choice of widescreen, letter
box and pan & scan video formats.
- Audio in up to 8 languages
- Subtitles for a further 32
- Menus and program chains for
- Up to 9 camera angles to give
the user more choice
- Digital and analogue copy
- Parental control for protection
Most DVD-Videos also include extras
that cannot be included on a VHS movie, such as biographies, director's
commentary, making of the movie etc. An increasing number
include DVD-ROM content, which can range from links to relevant
websites to a full game based on the movie. The use of
websites can allow the disc to be used in different ways with
updated text and graphics information on the website complementing
the video on the disc.
The DVD-Video specification is
based on a pre-recorded DVD (DVD-ROM) with UDF
Bridge file system. A DVD-Video can therefore be a DVD-5, DVD-10
or DVD-9 disc depending on the playing time required and other
For overall playing times longer
than 133 minutes (including additional content), the dual layer
DVD-9 offers a solution.
A DVD-10 is more useful where
widescreen and pan & scan versions are required on the same
disc. The use of the DVD-10 format is not recommended for longer
playing times, as the disc needs to be flipped to play the other
DVD and CD : What is the
|Data Storage: DVD vs. CD
DVD can store more data than CD for a few reasons:
- Higher-density data storage
- Less overhead, more area
- Multi-layer storage
Density Data Storage
Single-sided, single-layer DVD can store about seven times more data
than CD. A large part of this increase comes from the pits and
tracks being smaller on DVD.
Let's get an idea of how much more
data can be stored due to the physically tighter spacing of pits on
a DVD. The track pitch on a DVD is 2.16 times smaller, and the
minimum pit length for a single-layer DVD is 2.08 times smaller than
on a CD. By multiplying these two numbers, we find that there is
room for about 4.5 times as many pits on a DVD. So where does the
rest of the increase come from?
Overhead, More Area
On a CD, there is a lot of extra information encoded on the disc to
allow for error correction -- this information is really just a
repetition of information that is already on the disc. The error
correction scheme that a CD uses is quite old and inefficient
compared to the method used on DVD. The DVD format doesn't waste as
much space on error correction, enabling it to store much more real
information. Another way that DVDs achieve higher capacity is by
encoding data onto a slightly larger area of the disc than is done
on a CD.
To increase the storage capacity even more, a DVD can have up to
four layers, two on each side. The laser that reads the disc can
actually focus on the second layer through the first layer. Here is
a list of the capacities of different forms of DVDs:
You may be wondering why the
capacity of a DVD doesn't double when you add a whole second layer
to the disc. This is because when a disc is made with two layers,
the pits have to be a little longer, on both layers, than when a
single layer is used. This helps to avoid interference between the
layers, which would cause errors when the disc is played.
What is DVD?
DVD stands for both Digital Video
Disk and Digital Versatile Disk. This is because the format,
although initially used as a home video medium, has a wide variety
of potential applications.
A Format for Multiple Purposes:
For a long time technical pundits
have predicted that the computer, television, audio equipment, etc.
would converge into a common format. DVD is the fulfillment of this
prediction. In addition to home video, the DVD format can be used
for storing data, dramatically increasing capacity over the current
CD-ROM. It will also extend the amount of music or audio stored on
an Audio CD. Other uses of DVD include interactive video, games,
photo, and more. DVD is truly a "versatile" format. The
consumer will no longer need separate hardware to play both video
and audio discs. And he can attach the DVD player to a computer to
access high capacity DVD-ROM.
A Wealth of Features:
The DVD format will provide a list
of features unprecedented in the history of consumer electronics.
These include multiple soundtracks, subtitles, aspect formats, MPAA
versions and film releases on the same disc.
Backward Compatibility to Current
DVD also protects the consumer's
current investment in Audio CD, CD-ROM CDR, etc. The DVD players
will be able to play back these existing formats.
DVD players are priced in the $40
to $600 range, depending on features. Discs are priced from $7 to
$30 for feature films. The costs of replicating DVDs are
significantly less than for VHS tape or laser discs. The costs of
mastering, however, are much higher than for VHS tape, and somewhat
more than laser discs. This skews the economics of DVD in favor of
high volume, low priced DVD content. Replication of DVDs is faster
than VHS Tape. Under operation, a DVD replicator can produce one
disc every six seconds. Once a master has been encoded and cut, low
volume production runs can be easily accommodated. In summary, the
DVD format is priced at a level very attractive to consumers.
Picture and Sound Quality:
The quality of DVD is close to
source, D1, material; 720 pixels per horizontal line vs. 320 pixels
for VHS Tape. HDTV versions will have even greater resolution.
Because DVD is digital, the NTSC artifacts of analog formats are completely eliminated. DVD delivers outstanding picture clarity and
color sharpness. The DVD format provides multiple CD quality audio
with Dolby Digital, discrete 5.1 surround sound, to recreate the
theater experience in your own home.
The DVD disc is 4.8" in diameter (12cm), the same size as a compact
disc (CD). A 3"
(8cm) disc is also available.
Currently there have been seven DVD
formats, with various capacities, proposed. Those which have been
- SD5 4.7 GB, play only, single
sided, single layered
- SD9 8.5 GB, play only, single
sided, dual layered
- SD10 9.4 GB, play only, dual
sided, single layered (2 SD5s)
- SD18 17 GB, play only, dual
sided, dual layered
- SD-R 7.6 GB, Write once, dual
sided, single layered (WORM)
- SD-RAM 5.2 GB, Read/Write,
dual sided, single layered (Erasable)
- SD-HDTV 20+ GB, play only
using blue laser for higher disc capacity
The capacity of DVD will allow most
feature films to be recorded on single sided, single layer of a
disc. This eliminates the need to flip or change discs in the middle
of a film. Some of the movies that do not fit on a single sided,
single layer disc will require you to flip the disk over, like you
do with all laser disc. As more studios are putting movies that
exceed the 133 minuets on dual layer disc using RSDL (Reverse Spiral
Dual Layer) technology, a movie will be able to play seamlessly
without requiring to flip the disc over.
In the video studios' effort to prevent exporting,
discs manufactured in one region will only play on players
manufactured in that same region.
- Region 1: The U.S., its
territories and Canada
- Region 2: Europe, Japan, the
Middle East, Egypt, South Africa, Greenland
- Region 3: Taiwan, Korea, the
- Region 4: Mexico, South
America, Australia, New Zealand
- Region 5: Russia, Eastern
Europe, India, most of Africa
- Region 6: China
The Region Code is specified on the
back of the DVD package, either with a Regional Coding logo of a
globe with the region number superimposed on it or spelled out on the MGM discs: "This disc
has been encoded for region 1: The United States, U.S. territories
and Canada." Some discs have no regional coding--Lumivision
discs are labeled "Available worldwide," but some other
studios have not specified the Region Code one way or another.
AC-3, discrete digital 5.1 channel
CD quality sound with AC-3 surround
stereo has been adopted for the DVD format. Europe has adopted the
AC-3 sound also. It is hoped, however, that a single format will be
adopted worldwide, eliminating the need to produce two different
Multiple Sound Tracks:
DVD can include up to eight
separate AC-3 soundtracks to accommodate different languages or
other audio nuances. This allows multiple audio versions of a film
to be delivered on a single disc. Although most of the movies only
have one to three different language tracks, it depends on the
language within the region codes, for example region 1 will have an
English, French, and Spanish audio tracks. With extra room for audio
tracks some studios also have put audio commentaries with the movies,
this allows you to watch the movie while the director, talks about
Up to 32 subtitle tracks can be
stored on a single DVD. A viewer can choose the subtitle to be
displayed or suppress subtitles altogether. Subtitles are bit-mapped
so that non-ASCII characters, such as Asian languages, can be
accommodated. This will also allow overlays of graphics, such as a
grid or play diagrams, on the screen.
Features of Dolby AC-3 vs.
While Dolby Labs developed both
formats, Dolby Digital 5.1 sound is stored on six separate channels. This is
known as discrete 5.1 sound. There are five full range channels for
front (left, center and right) and rear (left and right) speakers,
plus a low frequency "woofer" channel. These signals are
amplified separately and sent to the speakers. The channels are
With Dolby Pro-Logic four channels (left, center, right and rear)
are matrixed into two standard stereo channels. The two rear
speakers receive a monaural, limited frequency range signal, these
are decoded upon playback into the four channels. With this format
there are some blending of the channels, resulting in a loss of
directional effects and a less dynamic recreation of the soundtrack.
Dolby Digital 5.1 is the true state of the art in creating the audio
ambiance of a movie theater in your home. Sounds can be placed and
moved anywhere in relationship to the listener; providing full 360
Aspect Ratio Support:
DVD format can contain 16x9,
Letterbox, and Pan & Scan formats on the same disk. Discs list the aspect ratios of the
Letterboxed transfers, whether 1.85:1 or 2.35:1. If the disc
contains a Pan & Scan transfer, that is also specified.
Some movies contain both Widescreen
and Pan & Scan versions on the same disc, they have the Letterbox
version on the A Side and the Pan & Scan version on the B Side.
Some discs feature the "dual-layer" format, where two sides
worth of programming can be read by the DVD player from one side of
the disc. When these discs are started, the viewer is first given an
on-screen option to choose the widescreen or full-screen version.
Because of the large quantities of
data stored on the disc for some of the longer films, a few discs
contain only one version of the film, either Letterbox or Pan &
few films will require using both sides; most films up to
approximately 2 hours 15 minutes or more will fit on one side of a
DVD. Unlike laserdisc, which has a strict time limit per side of 30
minutes for CAV and 60 minutes for CLV, DVD discs are limited by the
amount of data they can hold.
On DVD, 120 minutes of fast action,
spinning cameras and constantly changing visuals take up more disc
space than 120 minutes of stationary cameras and very little
on-screen movement. Studios are now starting to put movies
requiring two sides on one side using dual-layer discs, and that the
DVD player will be able to switch from one layer to the other
automatically and with little or no visible break.
Enhanced for 16x9 widescreen TV's
is the first video format (apart from a few Japanese laserdiscs) to
take full advantage of 16 x 9 TV capabilities, with these
"enhanced for 16 x 9" DVDs and the TV's special circuitry
squeezing more "lines of resolution" onto the screen than
a regular 4 x 3 TV set can.
A 4 x 3 aspect ratio TV set picture is made up
of approximately 480 horizontal lines of resolution from the top of
the screen to the bottom. A laserdisc or video tape letterboxed at
2.35:1 uses only around 270 of those lines of resolution to display
the picture; the other 210 lines make up the black bars you see at
the top and bottom of the screen.
On an "enhanced for 16 x
9" DVD disc (also known as an "anamorphic" DVD), that
same 2.35:1 letterboxed image is stretched vertically to use all 480
lines of resolution. (If you were to look at that image without any
further processing, all of the actors would appear unnaturally tall
and thin.) Then, the special circuitry in the 16x9 TV set squeezes
those 480 lines of picture back down to the proper size. In effect,
a picture that would be made up of 270 lines of resolution on a
regular 4 x 3 TV set is made up of a full 480 tightly-spaced lines
on a 16 x 9 set, resulting in finer detail than regular TVs can
MPAA Rating Control:
A single DVD disc can contain
multiple versions of a movie with different MPAA ratings. This
allows a viewer to select the version of the film he or she prefers.
For example, a viewer could choose the "R" or
"PG-13" version of a particular film. This feature also
allows parental lockout, so that a child or other person, without
the correct access code, could not view film versions above a
certain MPAA rating. Furthermore, this feature allows certain
countries to mandate that players sold in that country be outfitted
with a chip which prohibits viewing of films above a certain MPAA
rating. This eliminates the need to produce different versions of a
film with different MPAA ratings for countries with content
restrictions. When played, certain scenes will be skipped or
alternative scenes shown according to the MPAA rating chosen. This
"editing" occurs seamlessly without interruption of the
playback. However no studio has yet implemented this feature, but
Columbia Tri-Star do offer the parental lockout on some titles.
Multiple Film Versions:
DVD allows multiple versions of a
film to be recorded on a single disc. For example a disc could
contain both the theatrical and "director's cut" of a
movie. The user could then choose which version of the film to
watch. When played, certain scenes will be skipped or alternative
scenes shown according to the film version chosen. This
"editing" occurs seamlessly without interruption of the
playback. However there are many director’s cut titles on DVD, no
title has the option of choosing one or the other.
Audio-CD and CD-ROM Compatibility:
Audio DVD. This audio format with
higher fidelity and capacity than the current audio CD format is
available. Current audio CDs can be played on DVD players. DVD-ROM
will provide a more than ten-fold increase in capacity over current
CD-ROM discs. DVD players playback current CD discs.
DVD players are ranging from $35 to over $400 depending on the features. DVD
disc prices range from $5 to $25
for most feature films. These prices make DVD very
competitive to other video formats.
Other DVD Uses:
DVD-Interactive will allow games to
be distributed on DVD format. The higher capacity will allow better
graphics and more sophisticated games to be designed. DVD-Photo will
accommodate stock photographs to be distributed with greater
resolution and capacity then current CD-ROM formats. This may allow
the migration from film to electronic storage of photographs.
The History of DVD
started in 1994 and the format was launched in 1996. Since
then new formats and revisions have appeared.
ad hoc committee defined features for movies on a 'compact
announced and demonstrate MMCD.
Toshiba & Warner announce and demonstrate SD.
is reached on a single standard format called DVD that
combines the best of MMCD and SD.
and DVD-Video specifications version 1.0 published.
copy protection scheme (CSS) agreed.
players sold in Tokyo (Nov).
DVD in USA (Aug). DVD-R release followed.
Consortium becomes DVD Forum, expands membership and holds
first General DVD Forum Meeting with 120 members
version 1.1 and DVD-ROM version 1.01 specifications released.
announces 7 new members of DVD steering committee making 17 in
publishes DVD-Audio (version 0.9) specification
launch of DVD in Europe
1m DVD-Video players sold in USA
DVD-R and DVD-RAM version 1.9 specifications released
(1.0), DVD-Video Recording (0.9 & 1.0), DVD-RW (0.9) and
DVD-RAM (2.0) specifications published.
protection for DVD-Audio agreed
players launched in USA (Jul)
discs in USA (Nov)
Part 2 (1.0), DVD-R for Authoring (2.0), DVD-R for General
(2.0) and DVD Stream Recording (0.9) specifications published.
players & discs available
Recorders launched in Europe etc
(1.0), DVD Stream Recording (1.0), DVD-Audio (1.2) and DVD-Video
Recording (1.1) specifications published.
for IEEE 1394 transmission for DVD-Video/Audio issued.
created to study future blue laser format
recording specification ver 0.9 issued. DVD+R
DVD-Audio format considered by DVD Forum
rejects hybrid DVD-Audio format
releases iDVD specifications to provide more interactivity for
|DVD High-Definition formats Blu-ray and HD-DVD compete for
eventual market dominance.
|DVD Universal players available which can play DVD Video,
DVD Audio, SACD, CD and more.
|DVD recorders prices fall. DVD blank media DVD-R, DVD+R,
DVD-RW and DVD+RW prices fall.