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| The DVD is the latest and most powerful implementation
of optical media since the music CD in 1982. Capable of holding
7- to 12-times more data than the compact disc, DVD uses a system
with a highly efficient modulation scheme -- 8 to 16 EFM PLUS
-- that ensures backward compatibility with current discs as
well as with future rewritable media. Home video and computer
read portable data are offered record-breaking increased quality
and extension through DVD.
The DVD shares the same physical dimensions and durability
as its predecessor, which allows for instant familiarity with
its handling and storage. Its players and ROM drives are compatible
with existing music CDs and CD-ROMs. This means that one machine,
the DVD player, can be used to play video or music at home.
Like the CD, the DVD delivers data from one side, and allows
split-second random access.
Optical discs use microscopically engraved pits along tracks
to contain the digital information that is then played back
through a system that allows us to comprehend it visually or
audibly. DVD uses smaller pits and tighter tracks to produce
a significant increase in digital data. This requires the new
DVD players and ROM drives to use a laser that emits red light
at 650 and 635 nanometers. The laser assembly is further refined
with a higher Numerical Aperture lens, which results in a more
narrowly focused beam. Its error correction system, the Reed
Solomon Product Code, is approximately 10 times more powerful
than what is currently used with CD.
DVD comes either single-layered or double-layered. The single-layered
disc holds 4.7 gigabytes of digital data, seven times that of
the 680 megabyte capacity of the CD. The double-layered disc
increases capacity to 8.5 gigabytes, nearly a dozen times higher
than CD. The double-layered discs deeper layer of data is read
first by the laser which changes incomprehensibly to a shallower
focus to read the top layer when needed. A time buffer determines
seamless playback between the layers.
The DVD standard, CCIR-601, specifies a video data rate of
167 megabits per second. Since this translates into about four
minutes of digital video for a single layer DVD, the powerful
MPEG2 compression format is used for digital encoding. This
involves a two-stage process that very effectively allows complex
pictures to be assigned high bit rates and the profusely common
simple pictures are given low bit rates. The average bit rate
for digital video is usually given at 3.5 megabits per second.
In actuality, bit rates vary according to movie length, picture
complexity and the number of audio channels used.
Due to the dynamic compression of MPEG2, a single-layer DVD
is capable of two hours and 13 minutes of video and still allows
for 5.1-channel digital sound in three languages, and subtitles
in up to four. At this capacity, a DVD movie's data rate averages
4.962 megabits per second. Movie DVDs released in the U.S. will
be capable of supporting the high quality Dolby AC-3 digital
audio sound tracks with 2 or 5.1 channels. Producers may choose
16-bit linear, CD quality stereo sound with Dolby Pro Logic
encoding. DVD movies are also capable of including up to eight
languages and 32 sets of subtitles.
DVD-ROM capabilities will meet the ever increasing computer
processing power and software expansion we witness each day.
Its uses in databases, multimedia creation, educational programs
and video games pushes todays limits to broader boundaries.
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| As the compact disc has become so successful
and fulfils a wide range of applications, why has a new technology
been introduced and who needs it? Major companies from different
industries have invested heavily in developing DVD.
| The Format |
Who Needs
it? |
| DVD-Video |
The movie industry,
which needs a CD-like disc capable of holding a full length
movie of Laserdisc quality video with surround sound audio. |
| DVD-ROM |
The computer industry,
which is choosing DVD-ROM drives to be included in most
new PCs as these will also read CD-ROM discs as well as
DVD-ROMs. The entertainment industry, which has developed
new games consoles (eg Sony's PS2 and Microsoft's X-Box),
which incorporate DVD-ROM drives for more sophisticated
and realistic games. |
| DVD-Audio |
The music industry
because DVD-Audio offers the highest audio quality plus
surround sound and therefore a new, purer consumer experience. |
| DVD-RAM, DVD-RW & DVD-R |
The computer and
consumer electronics industries have already started
to introduce recordable DVD hardware on the market for PC
and video recording applications. |
DVD technology offers an optical disc with a much larger capacity
than the compact disc which is available as a family of pre-recorded,
recordable and re-writable formats to meet the requirements
of the industries mentioned above. |
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| DVD started as the Digital Video Disc but now
means Digital Versatile Disc or just DVD. It is a multi-application
family of optical disc formats for read-only, recordable and
re-writable applications.
The main features of the DVD formats are: |
| Backwards
compatibility with current CD media. All DVD hardware
will play audio CDs and CD-ROMs (although not all hardware
will play CD-Rs or CD-RWs).
Physical dimensions identical to compact
disc but using two 0.6 mm thick substrates, bonded together.
Single-layer/dual-layer and single/double
sided options.
Up to 4.7 GB read-only capacity per layer,
8.5 GB per side maximum.
Designed from the outset for video, audio
and multimedia, not just audio.
DVD-Video for full length movies with high
quality video on one disc.
DVD-ROM for enhanced multimedia and games
applications.
DVD-Audio for higher quality music, surround
sound and optional video, graphics and other features.
All formats use a common file system (UDF).
Digital and analogue copy protection for
DVD-Video and DVD-Audio built into standard.
Recordable and re-writable versions are part
of the family. |
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| DVD started in 1994 as two competing formats,
Super Disc (SD) and Multimedia CD (MMCD). DVD now is the result
of an agreement by both camps on a single standard to meet the
requirements of all the various industries involved. |
| Year |
Events |
| 1994
|
Hollywood
ad hoc committee defined features for movies on 'CD' .
|
| 1995
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Philips/Sony
announced and demonstrate MMCD Toshiba & Warner announce
and demonstrate SD
Agreement on a single standard format called DVD |
| 1996
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DVD-ROM
and DVD-Video specifications version 1.0 published
Digital copy protection scheme (CSS) agreed
First DVD-Video players sold in Tokyo (Nov) |
| 1997
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Launch of
DVD in USA (Aug)
DVD Consortium becomes DVD Forum, expands membership and
holds first General DVD Forum Meeting with 120 members
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| 1998
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DVD-Video
version 1.1 and DVD-ROM version 1.01 specifications released
DVD Forum adopts DVD-RW
DVD Forum announces 7 new members of DVD steering committee
making 17 in all
DVD Forum publishes DVD-Audio (0.9) specification
Full launch of DVD in Europe 1m DVD-Video players sold in
USA
4.7 GB DVD-R and DVD-RAM version 1.9 specifications released
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| 1999
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DVD-Audio
(1.0), DVD-Video Recording (0.9 & 1.0), DVD-RW (0.9) and
DVD-RAM (2.0) specifications published. |
| 2000
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CPPM copy
protection for DVD-Audio agreed
DVD-Audio players launched in USA (Jul)
First DVD-Audio discs in USA (Nov)
DVD-RW Part 2 (1.0), DVD-R for Authoring (2.0), DVD-R for
General (2.0) and DVD Stream Recording (0.9) specifications
published.
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| 2001
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DVD-Audio
players & discs available in Europe and elsewhere
DVD Video Recorders launched in Europe etc
DVD-Multi (1.0), DVD Stream Recording (1.0), DVD-Audio (1.2)
and DVD-Video Recording (1.1) specifications published.
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DVD discs come in a range of different physical formats
with capacities from 4.7 GB to 17.0 GB |
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| DVD discs have the same physical dimensions
as CDs, but each DVD comprises two substrates each 0.6mm thick
and bonded together like a sandwich.
This offers the possibility of discs with up to two sides and
up to two layers offering four possible read-only formats plus
recordable and rewritable formats: |
| Name |
Capacity
(GB) |
Layers |
Sides |
Comments |
| DVD-5 |
4.7 |
1 |
1 |
Read from
one side only |
| DVD-9 |
8.54 |
2 |
1 |
Read from
one side only |
| DVD-10 |
9.4 |
1 |
2 |
Read from
both sides |
| DVD-18* |
17.08 |
2 |
2 |
4 layers,
ead from both sides |
| DVD-R |
4.7/9.4 |
1 |
1 or 2 |
Recordable
DVD |
| DVD-RAM |
2.6/5.2 |
1 |
1 or 2 |
Rewritable DVD |
| DVD-RW |
4.7 |
1 |
1 or 2 |
Re-recordable DVD |
* DVD-18 is difficult to manufacture and , as it
is a double-sides format, there is little room for a lable and
the disc needs to be turned over to play both sides. NOTE: Crystal
Clear DVDs does not offer DVD-18 manufacturing. |
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| Each layer of a DVD disc contains lead-in,
data area and lead-out like a CD. For dual layer (DVD-9) discs
the two layers comprise a single volume, but can be organised
in two different ways depending on the application: |
|
Parallel Track Path PTP), where the
two layers both start at the inside diameter (ID) and
end at the OD with the lead-out. This is suitable for
DVD-ROM.
Opposite Track Path (OTP), where layer
0 starts at the ID and layer 1 starts where layer 0 ends.
For such discs there is one lead-in (on layer 0), one
lead-out (on layer 1) and two middle areas. This is suitable
for DVD-Video where a single movie can occupy both layers
with a layer break in the middle. Using OTP allows a near
seamless jump from layer 0 to layer 1.
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| These layouts for single and
dual layer discs are illustrated below.
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| DVD-5 (4.7GB) Single Sided/Single
Layer
This is the simplest of the family of DVD discs, comprising
a single layer with a capacity of 4.7GB. Only one of the two
0.6mm substrates contains data, the other being a blank disc.
The two substrates are bonded together to form a 1.2mm thick
disc.
Single sided discs can be printed on by any conventional method
eg screen printing. Alternatively, the blank substrate can be
moulded with an image in its surface and then metalised to make
it visible. |
| DVD-9 (8.5GB) Single Sided/Dual
Layer
This dual-layer, single sided version has a capacity of 8.5GB
which is slightly less than twice the single layer version,
to make it easier for the second layer to be read. Pits on both
layers are 10 per cent longer than on a DVD-5 or DVD-10 disc.
Each layer is moulded in one substrate, the two substrates
being joined with an optically transparent bonding layer. These
discs can be printed after bonding in the conventional way. |
| DVD-10 (9.4GB) Double Sided/Single
Layer
This disc comprises two sides each single layer. It differs
from the DVD-5 version in that both substrates contain data.
To read both sides the disc will need to be turned over for
most DVD players/readers. The capacity is 9.4GB, twice the single
side/single layer version.
Double sided discs cannot be printed except on the hub inside
the lead-in area. Labelling is therefore a problem with such
discs. |
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