DVD

Un article de Vev.

Modèle:Infobox media

DVD (also known as "Digital Versatile Disc" or "Digital Video Disc" - see Etymology) is a popular optical disc storage media format. Its main uses are video and data storage. Most DVDs are of the same dimensions as compact discs (CDs) but store more than 6 times as much data.

Variations of the term DVD often describe the way data is stored on the discs: DVD-ROM has data which can only be read and not written, DVD-R and DVD+R can be written once and then functions as a DVD-ROM, and DVD-RAM, DVD-RW, or DVD+RW holds data that can be erased and thus re-written multiple times.

DVD-Video and DVD-Audio discs respectively refer to properly formatted and structured video and audio content. Other types of DVD discs, including those with video content, may be referred to as DVD-Data discs. The term "DVD" is commonly misused to refer to high density optical disc formats in general, such as Blu-ray and HD DVD.

History

Modèle:Optical disc authoring

In 1993, two high-density optical storage standards were being developed; one was the MultiMedia Compact Disc, backed by Philips and Sony, and the other was the Super Density disc, supported by Toshiba, Time Warner, Matsushita Electric, Hitachi, Mitsubishi Electric, Pioneer, Thomson, and JVC. IBM's president, Lou Gerstner, acting as a matchmaker, led an effort to unite the two camps behind a single standard, anticipating a repeat of the costly videotape format war between VHS and Betamax in the 1980s.

Philips and Sony abandoned their MultiMedia Compact Disc and fully agreed upon Toshiba's SuperDensity Disc with only one modification, namely changing to EFMPlus modulation. EFMPlus was chosen as it has a great resilience against disc damage such as scratches and fingerprints. EFMPlus, created by Kees Immink, who also designed EFM, is 6% less efficient than the modulation technique originally used by Toshiba, which resulted in a capacity of 4.7 GB as opposed to the original 5 GB. The result was the DVD specification, finalized for the DVD movie player and DVD-ROM computer applications in December 1995.<ref name="uni_PR"> DVD Format Unification (press release)

. TOSHIBA 
 
 (December 8, 1995)
   

. Retrieved on 2007-07-12. </ref> In May 1997, the DVD Consortium was replaced by the DVD Forum, which is open to all other companies.

Etymology

"DVD" was originally used as an initialism for the unofficial term "digital video disc".<ref> A Battle for Influence Over Insatiable Disks

. New York Times 
 
 (1995-01-11)
   

. Retrieved on 2007-04-09. </ref> It was reported in 1995, at the time of the specification finalization, that the letters officially stood for "digital versatile disc" (due to non-video applications),<ref> DVD designers go with AC-3 Final specs for 'digital versatile disc'...

. The Hollywood Reporter 
 
 (1995-12-11)
   

. Retrieved on 2007-04-16. </ref> however, the text of the press release announcing the specification finalization only refers to the technology as "DVD", making no mention of what (if anything) the letters stood for.<ref name="uni_PR"/> A newsgroup FAQ written by Jim Taylor (a prominent figure in the industry) claims that four years later, in 1999, the DVD Forum stated that the format name was simply the three letters "DVD" and did not stand for anything.<ref> DVD FAQ

. DVD Demystified 
 
 (2006-09-12)
   

.</ref> The official DVD specification documents have never defined DVD. Usage in the present day varies, with "DVD", "Digital Video Disc", and "Digital Versatile Disc" being the most common.

DVD disc capacity

The 12 cm type is a standard DVD, and the 8 cm variety is known as a mini-DVD. These are the same sizes as a standard CD and a mini-CD.

Note: GB here means gigabyte in the SI sense, i.e. 10⁹ (or 1,000,000,000) bytes; while GiB is used for gibibyte, equal to 2³⁰ (or 1,073,741,824) bytes.

Example: A disc with 8.5 GB capacity is equivalent to: (8.5 × 1,000,000,000) / 1,073,741,824 ≈ 7.92 GiB.

Each DVD sector contains 2418 bytes of data, 2048 bytes of which are user data.

Capacity Note: There is a small difference in capacity (storage space) between + and - DL DVD formats. For example, the 12 cm single sided disc has capacities:

Capacity nomenclature

The five basic types of DVD are referred to by their approximate capacity in gigabytes.

. AfterDawn Ltd.  
 

 

Technology

DVD uses 650 nm wavelength laser diode light as opposed to 780 nm for CD. This permits a smaller spot on the media surface (1.32 µm for DVD versus 2.11 µm for CD).

Writing speeds for DVD were 1×, that is 1350 kB/s (1318 KiB/s), in the first drives and media models. More recent models at 18× or 20× have 18 or 20 times that speed. Note that for CD drives, 1× means 153.6 kB/s (150 KiB/s), 9 times slower. DVD FAQ

DVD recordable and rewritable

Main article: DVD recordable

HP initially developed recordable DVD media from the need to store data for back-up and transport.

DVD recordables are now also used for consumer audio and video recording. Three formats were developed: DVD-R/RW (minus/dash), DVD+[[DVD+R|R]]/[[DVD+RW|RW]] (plus), DVD-RAM.

Dual layer recording

Dual Layer recording allows DVD-R and [[DVD+R]] discs to store significantly more data, up to 8.5 Gigabytes per side, per disc, compared with 4.7 Gigabytes for single-layer discs. DVD-R DL was developed for the DVD Forum by Pioneer Corporation, [[DVD+R DL]] was developed for the DVD+RW Alliance by Philips and Mitsubishi Kagaku Media (MKM).<ref> Dual Layer Recording burnworld.com

. Retrieved on 2007-07-06. </ref>

A Dual Layer disc differs from its usual DVD counterpart by employing a second physical layer within the disc itself. The drive with Dual Layer capability accesses the second layer by shining the laser through the first semi-transparent layer. The layer change mechanism in some DVD players can show a noticeable pause, as long as two seconds by some accounts. This caused more than a few viewers to worry that their dual layer discs were damaged or defective, with the end result that studios began listing a standard message explaining the dual layer pausing effect on all dual layer disc packaging.

DVD recordable discs supporting this technology are backward compatible with some existing DVD players and DVD-ROM drives.<ref> Backwards Compatible burnworld.com

. Retrieved on 2007-07-06. </ref> Many current DVD recorders support dual-layer technology, and the price is now comparable to that of single-layer drives, though the blank media remains more expensive. The recording speeds reached by dual-layer media are still well below those of single-layer media.

DVD-Video

Main article: DVD-Video

DVD-Video is a standard for storing video content on DVD media. In the U.S., weekly DVD-Video rentals first out-numbered weekly VHS cassette rentals in June 2003, illustrating the rapid adoption rate of the technology in the marketplace.<ref> Bakalis , Anna

     (2003-06-20)
   
.    It's unreel: DVD rentals overtake videocassettes 
. Washington Times 
   

.</ref>

Though many resolutions and formats are supported, most consumer DVD-Video discs use either 4:3 or anamorphic 16:9 aspect ratio MPEG-2 video, stored at a resolution of 720×480 (NTSC) or 720×576 (PAL) at 29.97 or 25 FPS. Audio is commonly stored using the Dolby Digital (AC-3) or Digital Theater System (DTS) formats, ranging from 16-bits/48kHz to 24-bits/96kHz format with monaural to 7.1 channel "Surround Sound" presentation, and/or MPEG-1 Layer 2. Although the specifications for video and audio requirements vary by global region and television system, many DVD players support all possible formats. DVD-Video also supports features like menus, selectable subtitles, multiple camera angles, and multiple audio tracks.

DVD-Audio

Main article: DVD-Audio

DVD-Audio is a format for delivering high-fidelity audio content on a DVD. It offers many channel configuration options (from mono to 7.1 surround sound) at various sampling frequencies (up to 24-bits/192kHz versus CDDA's 16-bits/44.1kHz). Compared with the CD format, the much higher capacity DVD format enables the inclusion of considerably more music (with respect to total running time and quantity of songs) and/or far higher audio quality (reflected by higher linear sampling rates and higher vertical bit-rates, and/or additional channels for spatial sound reproduction).

Despite DVD-Audio's superior technical specifications, there is debate as to whether the resulting audio enhancements are distinguishable in typical listening environments. DVD-Audio currently forms a niche market, probably due to the very sort of format war with rival standard SACD that DVD-Video avoided.

Security

Main article: CPRM

DVD-Audio discs employ a robust copy prevention mechanism, called Content Protection for Prerecorded Media (CPPM) developed by the 4C group (IBM, Intel, Matsushita, and Toshiba).

To date, CPPM has not been "broken" in the sense that DVD-Video's CSS has been broken, but ways to circumvent it have been developed.<ref> DVD-Audio's CPPM can be got around with a WinDVD patch

. Retrieved on 2007-07-06. </ref> By modifying commercial DVD(-Audio) playback software to write the decrypted and decoded audio streams to the hard disk, users can, essentially, extract content from DVD-Audio discs much in the same way they can from DVD-Video discs.

Competitors and successors

There are several possible successors to DVD being developed by different consortia. Sony/Panasonic's Blu-ray Disc (BD) and Toshiba's HD DVD began to gain traction in 2007, and next-generation technologies such as Maxell's Holographic Versatile Disc (HVD) and 3D optical data storage are being actively developed.

On November 19, 2003, the DVD Forum decided by a vote of eight to six that HD DVD will be its official HD successor to DVD^{[citation needed]}. In spite of this, both BD and HD DVD have already severely hampered the adoption of any successor to DVD through a lack of the very cooperation that fostered DVD's success.

See also

References

• Bennett , Hugh

     (April 2004)
   
.    Understanding Recordable & Rewritable DVD 
. Optical Storage Technology Association 
   

. Retrieved on 2006-12-17.

• Labarge, Ralph. DVD Authoring and Production. Gilroy, Calif.: CMP Books, 2001. ISBN 1-57820-082-2.
• Taylor, Jim. DVD Demystified, 2nd edition. New York: McGraw-Hill Professional, 2000. ISBN 0-07-135026-8.

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External links

Modèle:Wikibookspar

Official

• DVD Forum
• DVD+RW Alliance
• DVD Copy Control Association and the Content Scramble System (CSS)

Quality guide

• Dual Layer Explained – Informational Guide to the Dual Layer Recording Process

Knowledge

• Blank media quality guide & FAQ
• Understanding Recordable & Rewritable DVD by Hugh Bennett
• DVD Frequently Asked Questions (and Answers)
• DVDs: in the fast lane
• History of DVD technology from the Consumer Electronics Association
• How Stuff Works - DVDaf:DVD

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