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DVD, which stands for Digital Video Disc,
Digital Versatile Disc, or nothing, depending on whom you ask, is
the next generation of optical disc storage technology. It's
essentially a bigger, faster CD that can hold video as well as
audio and computer data. DVD aims to encompass home entertainment,
computers, and business information with a single digital format,
eventually replacing audio CD, videotape, laserdisc,
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CD-ROM,
and perhaps even video game cartridges. DVD has widespread support
from all major electronics companies, all major computer hardware
companies, and about half of the major movie and music studios,
which is unprecedented and says much for its chances of success.
There's also the DVD-Audio format that was introduced in 1999.
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Features of DVD-Video
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Over 2 hours of high-quality digital video (over 8
on a double-sided, dual-layer disc).
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Support for widescreen movies on standard or
widescreen TVs (4:3 and 16:9 aspect ratios).
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Up to 8 tracks of digital audio (for multiple
languages, DVS, etc.), each with as many as 8 channels.
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Up to 32 subtitle/karaoke tracks.
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Automatic "seamless" branching of video
(for multiple story lines or ratings on one disc).
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Up to 9 camera angles (different viewpoints can be
selected during playback).
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Menus and simple interactive features (for games,
quizzes, etc.).
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Multilingual identifying text for title name, album
name, song name, cast, crew, etc.
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"Instant" rewind and fast forward,
including search to title, chapter, track, and timecode.
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Durable (no wear from playing, only from physical
damage).
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Not susceptible to magnetic fields. Resistant to
heat.
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Compact size (easy to handle, store, and ship;
players can be portable; replication is cheaper).
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Noncomedogenic.
Note: Most discs do not contain all features (multiple
audio/subtitle tracks, seamless branching, parental control, etc.), as
each feature must be specially authored. Some discs may not allow
searching or skipping.
Most players support a standard set of features:
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Language choice (for automatic selection of video
scenes, audio tracks, subtitle tracks, and menus).*
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Special effects playback: freeze, step, slow, fast,
and scan (no reverse play or reverse step).
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Parental lock (for denying playback of discs or
scenes with objectionable material).*
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Programmability (playback of selected sections in a
desired sequence).
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Random play and repeat play.
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Digital audio output (PCM stereo and Dolby
Digital).
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Compatibility with audio CDs.
* Must be supported by additional content on the disc.
Playing DVD movies on a computer
The computer operating system or playback software must
support regional codes and be licensed to descramble copy-protected
movies. If the computer has TV video out, it must support Macrovision in
order to play copy-protected movies. You may also need software that can
read the MicroUDF file system format used by DVDs. In addition to a
DVD-ROM drive you must have extra hardware to decode MPEG-2 video and
Dolby Digital or MPEG-2 audio, or your computer must be fast enough to
handle software decoding. Decent software-only playback requires a
Pentium II or higher. Hardware upgrade kits can be purchased for
existing computers (usually minimum 133 MHz Pentium
and an IDE/SCSI DVD-ROM drive with
bus mastering DMA to achieve about 24-30 frames/sec film rates). DVD-ROM
also includes recordable variations (DVD-R, DVD-RAM, DVD-RW, DVD+RW). Most
people expect DVD-ROM to be initially much more successful than DVD-Video.
Certain MPEG decoding tasks such as motion compensation
and IDCT (inverse discrete cosine transform) can be performed by
additional circuitry on a video graphics card, improving the performance
of software decoders. This is called hardware decode acceleration or
hardware motion comp.
Microsoft Windows 98 includes DirectShow
5.2, which provides standardized support for DVD-Video and MPEG-2
playback. DirectShow can also be installed in Windows 95. DirectShow 6.0
is available for download.
DirectShow provides a standardized framework for DVD playback, but a
third-party hardware or software decoder is still required (see below).
Windows NT 4.0 supports DVD-ROM drives for data, but has very little
support for playing DVD-Video discs. Windows 2000 will use the same WDM
drivers and DirectShow software as Windows 98. Internet Explorer 5.0
includes a new version of Windows
Media Player that enables scriptable DVD playback in an HTML page.
Windows 98 and newer can read UDF discs. Adaptec
provides a free filesystem driver, UDF Reader, for Windows 95/98/NT. Software
Architects sells Read DVD for Windows 95.
DVD player applications (using either software or
hardware decoding) are virtual DVD players. They support most DVD-Video
features (menus, subpictures, etc.) and emulate the functionality of a
DVD-Video player remote control. Many player applications include
additional features such as bookmarks, chapter lists, and subtitle
language lists.
Video decoding: Software vs.
hardware
Software decoders and DVD player applications for
Microsoft Windows PCs are made by CyberLink
(PowerDVD), InterVideo,
Mediamatics (DVD
Express), MGI, NEC, Odyssey,
QI (Software CineMaster), Xing,
Zoran (SoftDVD), and
others. Only CyberLink, Odyssey, and Xing decoders are available for
retail purchase, the others are bundled with OEM DVD PCs. A special
low-cost version of the QI software decoder is available for download from
the ATI web site for
use with ATI video cards. CyberLink and Odyssey don't yet support
DirectShow.
Hardware decoder cards and DVD-ROM upgrade kits for
Microsoft Windows PCs are made by Creative
Technology (Encore, C-Cube chip), IBM
(ThinkPad laptops, IBM chip), LeadTek
(WinFast 3D S800, Mpact2 chip), Margi
(DVD-to-Go, ZV PC card for laptops), QI
(Hardware Cinemaster, C-Cube chip), Sigma
Designs (Hollywood, Sigma chip), STB
(DVD Theater, Mpact2 chip), Toshiba
(Tecra laptops, Toshiba chip), and others. The Sigma Designs decoder card
is used in decoder upgrade kits from Hitachi,
HiVal, Panasonic,
Phillips, Sony,
and Toshiba. The
advantage of hardware decoders is that they don't eat up CPU processing
power, and they often produce better quality video than software decoders.
If you want to hook a DVD computer to a TV, the decoder
card or the VGA card must have a TV output (composite video or s-video).
Alternatively, you can connect a scan converter to the VGA output. The
quality of the video will depend on the decoder, the TV encoder chip, and
other factors.
Features and speeds of PC DVD-ROM
drives
Unlike CD-ROM
drives, which took years to move up to 2x, 3x, and faster spin rates,
faster DVD-ROM drives began appearing in the first year. Most 1x DVD-ROM
drives have a seek time of 90-200 ms and access time of 100-250 ms. 1x
DVD-ROM drives provide a data transfer rate of 1.321 MB/s
(11.08*10^6/8/2^20) with burst transfer rates of up to 12 MB/s or higher.
The data transfer rate from a DVD-ROM disc at 1x speed is roughly
equivalent to a 9x CD-ROM drive (1x CD-ROM data transfer rate is 150 KB/s,
or 0.146 MB/s). DVD spin rate is about 3 times faster than CD (that is, 1x
DVD ~ 3x CD), but almost all DVD-ROM drives increase motor speed when
reading CD-ROMs, achieving 12x or faster performance. 2x DVD-ROM drives
are available (providing a transfer rate of 22.2 Mbps or 2.6 MB/s from
DVDs, equivalent to an 18x CD-ROM rate). Most 2x DVD-ROM drives read
CD-ROMs at 20x (max) speeds and higher. 4x, 4.8x, 5x, 6x, 8x, 10x, 12x and
16x drives are also available, although they usually don't achieve a
sustained transfer rate at their full rating. A 5x drive can theoretically
transfer data at 55.4 Mbps or 6.4 MB/s, equivalent to a 45x CD-ROM data
rate. Most 12x and faster DVD-ROM drives read CD-ROMs at 40x (max).
In order to maintain constant linear density, typical
CD-ROM and DVD-ROM drives spin the disc more slowly when reading near the
outside where there is more physical surface in each track. (This is CLV,
constant linear velocity.) Some faster drives keep the rotational
speed constant and use a buffer to deal with the differences in data
readout speed. (This is CAV, constant
angular velocity.) In CAV drives, the data is read fastest at the
outside of the disc, which is why specifications often list "max
speed."
Note: When playing movies, a fast DVD-ROM drive gains
you nothing more than possibly smoother scanning and faster searching.
Speeds above 1x do not improve video quality from DVD-Video discs. Higher
speeds only make a difference when reading computer data, such as when
playing a multimedia game or when using a database.
Connectivity is similar to that of CD-ROM drives: EIDE
(ATAPI), SCSI-2,
etc. All DVD-ROM drives have audio connections for playing audio CDs. No
DVD-ROM drives have been announced with DVD audio or video outputs (which
would require internal audio/video decoding hardware). In order to hook a
DVD-ROM PC to a television and a stereo receiver, the decoder card or the
video card must have a TV video output and an audio output. Some cards
have SP/DIF outputs to connect to digital audio receivers. If there's no
video output, a TV scan converter can be connected to the VGA
output.
Almost all DVD-Video and DVD-ROM discs use the UDF
Bridge format, which is a combination of the DVD MicroUDF and ISO 9660
file systems. The OSTA
UDF file system will eventually replace the ISO 9660 system originally
designed for CD-ROMs, but the bridge format provides backwards
compatibility until more operating systems support UDF.
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