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The notion of a high density
optical video disc was toyed with by numerous companies in
the late 1980s and early 1990s, but it wasn't until 1993
that the germ of what we know now as DVD began to grow. That
year British company Nimbus Technology and Engineering
demonstrated a slightly modified dual-speed Red Book (the
standard used by the CD format) disc using the recently
introduced MPEG-1 video compression system. This technique
permitted picture quality that was a significant improvement
from the single-speed MPEG-1 devices available at the time,
such as CDV (White Book) and CD-i (Green Book), but video
quality was still relatively poor and it became clear to
those involved that the future of video didn't lie with the
then decade-old Compact Disc platform. Later that year
Nimbus joined a consortium of other companies, headed by
giants Toshiba and Time Warner, that sought to develop this
next-generation video platform.
All parties in this consortium
had a vested interest in the future of home video,
from either a hardware or software perspective. Software developers had
been distinctly underwhelmed with the thought of a
next-generation video system that offered little more
performance than standard VHS and considerably lower video
and audio quality than the (even then) well-worn analogue
LaserDisc system. These same parties were also
understandably concerned that any next-generation format
also carry next-generation copyright protection. Hardware
producers felt that any new product would need to be a
significant improvement over any existing product in order
to generate hardware sales and attract buyers.
The following year a 'wish
list' of features to be included in this proposed format was
decided upon following the recommendations of an advisory
committee established by Hollywood's major players. This
committee recommended a system capable of producing at least
133 minutes of high quality video, stereo and multichannel
(six-channel) audio capabilities, multiple audio and
subtitle tracks, dual aspect ratio compatibility (1.78:1 and
1.33:1) and a series of advanced copy protection systems.
Things began to heat up in
December 1994 when Sony and Philips announced the
development of the MMCD (Multimedia CD) disc to meet these
requirements. MMCD discs held up to 3.6GB of data per layer
and used the better MPEG-2 video compression format. The
MMCD format also used numerous technologies that were
covered by Philips and Sony’s existing technology patents,
which would ensure a steady revenue stream for both parties
if adopted.
One month later in January
1995, Toshiba and Warner Brothers announced their response,
a format called SD (Super Density). SD's data capacity was
greater, up to 18Gb compared to MMCD's 7.4GB, and it was
based around technologies that weren’t covered by Sony or
Philips’ patents. In light of the potential profits
involved, neither consortium were willing to endorse the
others’ system and for the following nine months there was a
real possibility the introduction of a new high-quality
digital video/data format might dissolve into another
VHS/Beta war, or even grind to an unceremonious halt.
Luckily, growing press and industry concern eventually led
IBM and several of Hollywood’s major studios to step into
the fray and exert pressure on both sides to settle on a
common format. The studios had a vested interest in ensuring
the format was brought to the market within a reasonable
timeframe, and IBM were keen to ensure that any format
chosen was compatible with future IBM optical devices. This
pressure prompted a new round of talks resulting in a
compromise that satisfied all parties, and the new hybrid
format was settled on in September 1995 at the IFA in
Berlin.
At the same time a new
industry regulatory body, named the DVD Consortium, was
established consisting of all companies involved in the SD
and MMCD formats. The new format was formally announced in
December 1995. The new high density disc was officially
dubbed 'DVD', although exactly what these initials stood for
remained uncertain. The format’s specifications weren’t
finalised until September 1996 when the DVD-Video and
DVD-ROM Specifications Version 1.0 document was published.
The following month DVD-Video's copy protection was
finalised, paving its way for release.
The new DVD format was much closer to the Toshiba SD
proposal than the MMCD system (the DVD format is,
essentially, a tweaked variant of the SD format),
incorporating multiple bonded layers, dual sided disc
capability and up two data layers per disc side. Several
Sony/Philips elements, such as their MMCD format’s signal
modulation system were added to the format, ensuring that
all parties would get a piece of the royalties pie, but
little of MMCD's fundamental technology was transferred into
the DVD format. In November 1996 the first DVD players went
on sale in Japan, and a few months later in March 1997 made
their US debut. As two of the major players behind the new
format were also major content producers, discs from Warner
Home Video and Columbia TriStar (owned by Sony) were
available for the format's introduction and bolstered the
format while the other studios dithered about support for
DVD. The rest, as they say, is history as the DVD went on to
become the most successful consumer electronics launch in
history, far exceeding the sales chalked up by the original
CD format back in 1982/3.
At first glance a CD and DVD
are very similar. Both are the same physical size (120mm in
diameter, 1.2mm in depth). That, however, is where the similarities
end. CDs consist of a single layer, whereas DVDs comprise
two 0.6mm bonded polycarbonate layers. The spirals of data
on a DVD are also more tightly packed and the data pit
length half that of a CD. As a result of these differences,
the laser used to read a DVD is much narrower (650/635nm as
opposed to 780nm on CD). DVDs also spin at more than twice
the speed of a CD. This speed increase and pit/spiral
difference results in a maximum data transfer-rate of up to
10.08Mbps from DVD-Video, over seven times the capability of CD at
1.4112Mbps.
DVDs come in a variety of sizes, or densities. The most
common are:
- DVD-5,
- DVD-10,
- DVD-9, and;
- DVD-18
The basic single layer,
single side variant is known as a DVD-5 and stores up to
4.7GB of data. Dual-sided DVD-5s are known as (surprise)
DVD-10s. A dual-layered single-sided DVD is known as a DVD-9
and contains up to 8.54GB of data. The second layer of data
on a
DVD-9 disc (called layer 1) contains slightly less
information that the first
layer (layer 0), as the data pits are spaced slightly
further apart. This increase allows more accurate reading of the
second layer through the first data layer and the
transparent glue used to bond the two data layers together.
A dual-layered, dual-sided disc is known as a DVD-18, and
can contain up to 17.08GB of data. DVD-18 discs use a slightly
different and much more difficult construction technique than
that used by DVD-5, 9 or 10 discs (see the
Home Theatre Glossary).
DVD-18 discs are still relatively uncommon due to limited
production facilities and higher production failure rates
caused by its manufacturing difficulty. Various other
densities are also available, including hybrid DVD/CDs and
DVD-14 dual-layer/single-layer hybrids, but these are
extremely uncommon.
Video on DVD-Video is
compressed using either the MPEG-1 or MPEG-2 video
compression format, although the use of MPEG-1 is extremely rare. The
maximum video bitrate for MPEG-2 compressed video content on DVD is 9.8Mbps
(megabits per second), with
possible frame sizes of up to 720x480 (width x height) pel (NTSC) or 720x576
pel (PAL). Supported frame rates are 24, 25 or 30fps (frames
per second). Horizontal picture
resolution on DVD is roughly twice that of VHS (240 NTSC,
260 PAL) and slightly better than LaserDisc (420 NTSC, 440
PAL).
Audio on DVD-Video is
presented via:
- PCM (Uncompressed. Up to 24-bit 96kHz
resolution, consuming 4.608Mbps),
- MPEG Multichannel (Up to
912kbps. Extremely uncommon and generally restricted to
European discs),
- DTS (Up to 1509kbps), or;
- Dolby Digital (Up to
448kbps).
PCM on DVD is able to
reproduce a maximum of eight channels of audio, but
currently available decoding hardware is generally only
designed for two-channel audio. DTS supports up to seven
channels, although commonly only six are used. Dolby Digital
currently supports up to six channels. Sony’s SDDS system is an optional
audio format, but has not been utilised and is unlikely to
be used in the future.
DVD-Video supports up to eight audio streams, comprising any
combination of the four main audio formats, although the
maximum data-rate available for all combined soundtracks is
6.144Mbps.
DVD-Audio uses a lossless compression system
developed by Boothroyd Stuart Meridian called Meridian
Lossless Packing or 'MLP'. This system is used to losslessly
store PCM audio at very high resolutions. MLP on DVD-Audio is capable of reproducing up to
two channels of 24-bit 192kHz resolution audio, vastly
superior to CD, consuming 9.22Mbps;
or up to six channels at 24-bit 96kHz resolution.
Up to 32 subtitle tracks may be included on a DVD, with four
colours available at any one time and a maximum subpicture
bitmap size of 720x576. Consequently, an entire frame may be
occupied by subpicture information if desired. This allows
elaborate fullscreen subtitled material, such as animated
text or graphics as used by New Line’s Infinifilm line and
Columbia TriStar’s Men in Black and Ghostbuster titles.
Active subtitles are also supported, allowing 'hotspot'
linking of text and graphics to various data sectors of a
disc (as used in Warner Brothers’ Matrix disc for its 'white
rabbit' feature, for example).
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