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DVD (sometimes known as "Digital Versatile Disc" or "Digital Video Disc") is an optical disc storage media format that can be used for data storage, including movies with high video and sound quality. DVDs resemble CDs as their physical dimensions are the same (12cm in diameter) but they are encoded in a different format and at a much higher density. The official DVD specification is maintained by the DVD Forum.

History

In the early 1990s two high density optical storage standards were being developed: one was the MultiMedia Compact Disc (MMCD), backed by Philips and Sony, and the other was the Super Density Disc (SD), 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 format war between VHS and Betamax in the 1980s.

Philips and Sony abandoned their MMCD format and agreed upon Toshiba's SD format with two modifications that are both related to the servo tracking technology. The first one was the adoption of a pit geometry that allows "push-pull" tracking, a proprietary Philips/Sony technology. The second modification was the adoption of Philips' Eight-to-Fourteen Modulation (EFMPlus). EFMPlus is 6% less efficient than Toshiba's SD code, which resulted in a capacity of 4.7GB instead of SD's original 5GB. The great advantage of EFMPlus is its great resilience against disc damage such as scratches and fingerprints. The result was the DVD specification Version 1.0, announced in 1995 and finalised in September 1996.

The first DVD players and discs were available in November 1996 in Japan, March 1997 in the United States, 1998 in Europe and in 1999 in Australia. The first pressed DVD was the movie Twister in 1996. The movie had the first test for 2.1 surround sound. The first titles released in the U.S., on March 19 1997, by Lumivision, authored by AIX Entertainment, were IMAX adaptations: Africa: The Serengeti, Antarctica: An Adventure of a Different Nature, Tropical Rainforest, and Animation Greats.

In 1999 DVDs represented only a small part of most shops video inventory; VHS tapes of movies made up the remainder.

As of 2005 the situation is now completely reversed; DVD sales make up the bulk of gross sales and VHS is a slim minority. The price of a DVD player has dropped to below the level of a typical VCR (although DVD recorders are still significantly more expensive than VCRs); a low-end player with reasonable quality can be purchased for under £50 in many retail stores and many modern computers are sold with DVD-ROM drives stock. Most, but not all, movie "sets" or series have been released in box sets, as have some entire seasons or selected episode volumes of older and newer television programs.

In 2000, Sony released its PlayStation 2 console in Japan. In addition to playing video games developed for the system it was also able to play DVD movies. This proved to be a huge selling point because the PS2 cost about the same as standard DVD players but could do a whole lot more. As a result, many electronic stores that normally did not carry video game consoles carried PS2s. In keeping with this tradition, Sony has announced that it will implement one of DVD's possible successors, Blu-ray, into the PlayStation 3.

Microsoft's Xbox, released a year after the PlayStation 2, also had the capability to play DVD discs with an add-on remote control kit, cementing the DVD's place in home consoles.

"DVD" was originally an initialism for "Digital Video Disc." Some members of the DVD Forum believe that it should stand for "Digital Versatile Disc" to reflect its widespread use for non-video applications. Toshiba, which maintains the official DVD Forum site [1], adheres to the interpretation of "Digital Versatile Disc." The DVD Forum never reached a consensus on the matter, however, and so today the official name of the format is simply "DVD"; the letters do not officially stand for anything.

Technical information

DVDs are made from a 0.6 mm thick disc of polycarbonate plastic coated with a much thinner reflective layer of aluminium or gold. Two such discs are glued together to form a 1.2 mm disc that can be designed to be read from one side (single sided) or both sides (double sided). The substrates are half as thick as a CD to make it possible to use a lens with a higher numerical aperture and therefore use smaller pits and narrower tracks.

A single-layer DVD can store 4.7 GB, which is around seven times as much as a standard CD-ROM. By employing a red laser at 650 nm wavelength (compared to 780 nm for CD) and a numerical aperture of 0.6 (compared to 0.45 for CD), the read-out resolution is increased by a factor 1.65. This holds for two dimensions, so that the actual physical data density increases by a factor of 3.5. DVD uses a more efficient coding method in the physical layer. CD's error correction, CIRC, is replaced by a powerful Reed-Solomon product code, RS-PC; Eight-to-Fourteen Modulation (EFM) is replaced by a more efficient version, EFMPlus, which uses eight-to-sixteen modulation. There is no subcode as in CD. As a result, the DVD format is 47 percent more efficient with respect to CD-ROM, which uses a "third" error correction layer.

There are a variety of application types for DVD:

  • DVD-Video (containing movies (video and sound))
  • DVD-Audio (containing high-definition sound)
  • SACD (containing high-definition sound)
  • DVD-VR (containing recorded video and sound, usually from TV or camcorder)
  • DVD+VR (a variation of DVD-Video used for recording on +R and +RW discs)
  • PS2 DVD (containing games for Playstation 2)
  • Xbox DVD (containing games for Xbox)
  • DVD-Data (containing data)

The disc medium can be:

  • DVD-ROM (read only, manufactured by a press)
  • DVD-R/RW (R = Recordable once, RW = Rewritable)
  • DVD-RAM (random access rewritable)
  • DVD+R/RW (R = Recordable once, RW = Rewritable)
  • DVD-R DL (dual layer record once)
  • DVD+R DL (double layer record once)

The disc may have one or two sides, and one or two layers of data per side; the number of sides and layers determines the disc capacity.

  • DVD-5: single sided, single layer, 4.7 GB
  • DVD-9: single sided, double layer, 8.5 GB
  • DVD-10: double sided, single layer on both sides, 9.4 GB
  • DVD-14: double sided, double layer on one side, single layer on other, 13.3 GB
  • DVD-18: double sided, double layer on both sides, 17.1 GB

The capacity of a DVD-ROM can be visually determined by noting the number of data sides, and looking at the data side(s) of the disc. Double-layered sides are usually gold-coloured, while single-layered sides are usually silver-coloured, like a CD. One additional way to tell if a DVD contains one or two layers is to look at the center ring on the underside of the disc. If there are two barcodes, it is a dual layer disc. If there is one barcode, there is only one layer.

Each medium can contain any of the above content and can be any layer type.

The DVD Forum created the official DVD-ROM/R/RW/RAM standards and the DVD+RW Alliance created the DVD+R/RW standards. Since DVD+R/RW discs are not technically DVDs as per the DVD Forum standards, they are not allowed to display the DVD logo; instead, they display an "RW" logo (even if it is not re-writeable, something some consider deceptive advertising). However, they are readable by most DVD drives, so they are referred to as DVD+R and DVD+RW.

The "+" and "-" are similar technical standards and are partially compatible. As of 2005, both formats are equally popular, with about half of the industry supporting "+", and the other half "-". Around 90% of DVD readers (drives and player) can read the recordable formats, with DVD-R having the best overall compatibility in independent tests. Almost all DVD writers can write both formats and carry both the +RW and DVD-R/RW logos.

Unlike compact discs, where sound is stored in a fundamentally different fashion than data, a properly authored DVD will always contain data in files readable by both the Universal Disk Format filesystem and the ISO 9660 filesystem (often called UDF Bridge format).

The reference data rate of DVD is 11.08 Mbps. The data transfer rate of a DVD drive is often given in multiples of 1352 KB/s, which means that a drive with 16x speed designation allows a data transfer rate of 16 × 1352 = 21640 KB/s (21.13 Mbps). As CD drive speeds are given in multiples of 150 KB/s, one DVD "speed" equals nine CD "speeds," so an 8x DVD drive should have a data transfer rate similar to that of a 72x CD drive. In physical rotation terms (spins per second), one DVD "speed" equals three CD "speeds," so an 8x DVD drive has the same rotational speed as 24x CD drive.

Early CD and DVD drives read data at a constant rate. The data on the disc is passed under the read head at a constant rate (Constant Linear Velocity). As linear (metres per second) track speed grows at outer parts of the disc proportionally to the radius, the rotational speed of the disc was adjusted according to which portion of the disc was being read. Most current CD and DVD drives have a constant rotation speed (Constant Angular Velocity). The maximum data rate specified for the drive/disc is achieved only at the end of the disc's track (discs are written from the inside). The average speed of the drive therefore equals to only about 50-70% of the maximum nominated speed. While this seems a disadvantage, such drives have a lower seek time as they do not have to change the disc's speed of rotation.

DVD-Video

DVD-Video discs require a DVD-drive with an MPEG-2 decoder (e.g. a DVD-player or a DVD computer drive with a software DVD player). Commercial DVD movies are encoded using a combination of MPEG-2 compressed video and audio of varying formats (often multi-channel formats as described below). Typical data rates for DVD movies range from 3-10 Mbps, and the bit rate is usually adaptive. The video resolution on NTSC discs is 720 × 480 and on PAL discs is 720 × 576. A high number of audio tracks and/or lots of extra material on the disc will often result in a lower bit rate (and image quality) for the main feature.

The audio data on a DVD movie can be of the format PCM, DTS, MP2, or Dolby Digital (AC-3). In countries using the NTSC standard any movie should contain a sound track in (at least) either PCM or Dolby AC-3 formats, and any NTSC player must support these two; all the others are optional. This ensures any standard compatible disc can be played on any standard compatible player. The vast majority of commercial NTSC releases today employ AC-3 audio.

Initially, in countries using the PAL standard (e.g. most of Europe) the sound of DVD was supposed to be standardised on PCM and MP2, but apparently against the wishes of Philips, under public pressure on December 5, 1997, the DVD Forum accepted the addition of Dolby AC-3 to the optional formats on discs and mandatory formats in players. The vast majority of commercial PAL releases employ AC-3 audio by now.

DVDs can contain more than one channel of audio to go together with the video content. In many cases, sound tracks in more than one language track are present (for example the film's original language as well as a dubbed track in the language of the country where the disc is being sold).

With several channels of audio from the DVD, the cabling needed to carry the signal to an amplifier or TV can occasionally be somewhat frustrating. Most systems include an optional digital connector for this task, which is then paired with a similar input on the amplifier. The selected audio signal is sent over the connection, typically over RCA connectors, in its original format to be decoded by the audio equipment. When playing compact discs, the signal is sent in S/PDIF format instead.

Video is another issue which continues to present problems. Current players typically output analogue video only, both composite video on an RCA jack, as well as S-Video in the standard connector. However neither of these connectors were intended to be used for progressive video, so yet another set of connectors has started to appear, to carry a form of component video, which keeps the three components of the video, one luminance signal and two colour difference signals, as stored on the DVD itself, on fully separate wires (whereas S-Video uses two wires, uniting and degrading the two colour signals, and composite only one, uniting and degrading all three signals). The connectors are further confused by using a number of different physical connectors on different player models, RCA or BNC, as well as using VGA cables in a non-standard way (VGA is normally analogue RGB—a different, incompatible form of component video). Even worse, there are often two sets of component outputs, one carrying interlaced video, and the other progressive. In Europe and other PAL areas, SCART connectors are typically used, which carry both composite and analog RGB interlaced video signals, as well as analogue two-channel sound on a single multiwire cable, and which offer a reasonable compromise between video quality—which is superior to S-Video though inferior to progressive component video —and cost. HDMI is a new connection similar to SCART, but it carries High Definition, Enhanced Definition and Standard Definition video. Along with video HDMI also supports up to eight-channel digital audio. Some HDMI-equipped DVD players can upconvert the video to higher definition formats such as 720p and, more rarely, 1080p.

DVD Video may also include one or more subtitle tracks in various languages, including those made especially for the hearing impaired. They are stored as images with transparent background which are overlaid over the video during playback. Subtitles are restricted to four colours (including transparency) and thus tend to look cruder than permanent subtitles on film.

DVD Video may contain Chapters for easy navigation (and continuation of a partially watched film). If space permits, it is also possible to include several versions (called angles) of certain scenes, though today this feature is mostly used—if at all—not to show different angles of the action, but as part of internationalisation to e.g. show different language versions of images containing written text, if subtitles will not do.

A major selling point of DVD Video is that its storage capacity allows for a wide variety of extra features in addition to the feature film itself. This can include audio commentary that is timed to the film sequence, documentary features, unused footage, trivia text commentary, simple games and film shorts.

Restrictions

DVD-Video has four complementary systems designed to restrict the DVD user in various ways: Macrovision, Content-Scrambling System (CSS), region codes, and disabled user operations (UOPs).

Content-scrambling system

Many DVD-Video titles use (CSS) encryption, which is intended to discourage people from bypassing the region control mechanism. Usually, users need to install software provided on the DVD or downloaded from the Internet such as WinDVD, PowerDVD, MPlayer, or VLC to be able to view the disc in a computer system.

The CSS has caused major problems for the inclusion of DVD players in any open source operating systems, since open source player implementations are not officially given access to the decryption keys or license the patents involved in the CSS. Proprietary software players were also difficult to find on some platforms. However, a successful effort has been made to write a decoder by reverse engineering, resulting in DeCSS. This has led to long-running legal battles and the arrest of some of those involved in creating or distributing the DeCSS code, through the use of the controversial U.S. Digital Millennium Copyright Act, on the grounds that such software could also be used to facilitate unauthorised copying of the data on the discs. But as U.S. law stops at the border of the United States, the rest of the world can enjoy de-scrambling software to bypass the DVD restrictions. A number of software programs have since appeared on the internet to view DVDs on a number of platforms.

The restrictions also prevent people from copying DVDs. In the past few years a large amount of software has been created to make copies such as DVD Shrink and DVD Decrypter.

Region codes

Each DVD-Video disc contains one or more region codes, denoting the area[s] of the world in which distribution and playback are intended. The commercial DVD-Video player specification dictates that a player must only play discs that contain its region code. In theory, this allows the motion picture studios to control the various aspects of a release (including content, date and price) on a region-by-region basis. In practice, many DVD players allow playback of any disc, or can be modified to do so. Entirely independent of encryption, region coding pertains to regional lockout, which originated in the video game industry.

Region code Area
0 Informal term meaning "playable in all regions"
1 Bermuda, Canada, United States and U.S. territories
2 The Middle East, Western Europe, Central Europe, Egypt, Greenland, Japan, Lesotho, South Africa and Swaziland
3 Southeast Asia, Hong Kong, Macau, South Korea and Taiwan
4 Central America, the Caribbean, Mexico, Oceania, South America
5 The rest of Africa, Former Soviet Union, the Indian subcontinent, Mongolia, North Korea
6 Mainland China
7 Reserved for future use
8 International venues such as aircraft, cruise ships, etc.
9 Pirated disc often purchased in the Middle East

European Region 2 DVDs may be sub-coded "D1" through "D4." "D1" identifies a UK-only release. "D2" and "D3" identify European DVDs that are not sold in the UK and the Republic of Ireland. "D4" identifies DVDs that are distributed throughout Europe.

Any combination of regions can be applied to a single disc. For example, a DVD designated Region 2/4 is suitable for playback in Western Europe, Oceania and any other Region 2 or Region 4 area. A so-called "Region 0" disc (actually coded Region 1/2/3/4/5/6) is meant to be playable worldwide.

The term "Region 0" also describes DVD players that were designed or modified to incorporate Regions 1-6 simultaneously, thereby providing compatibility with virtually any disc, irrespective of region[s]. This apparent solution was popular in the early days of the DVD format, but studios quickly responded by adjusting discs to refuse to play in such machines. This system is known as "Regional Coding Enhancement" or RCE.

Nowadays, many "multi-region" DVD players defeat regional lockout and RCE by automatically identifying and matching a disc's region code and/or allowing the user to manually select a particular region. Others simply bypass the region code check entirely. Some manufacturers of DVD players now freely supply information on how to disable regional lockout, and on some recent models, it appears to be disabled by default.

Many view region code enforcement as a violation of WTO free trade agreements; however, no legal rulings have yet been made in this area.

User operations

DVD-Video allows the disc to specify whether or not the user may perform any operation, such as selecting a menu, skipping chapters, forwarding or rewinding—essentially any function on the remote control. This is known as User Operation Prohibitions, or UOPs for short. Most DVD players respect these commands (e.g. by preventing fast-forwarding through a copyright message at the beginning of a disc), although some can be configured to ignore them, particularly open source player software.

DVD-Audio

Main article: DVD-Audio

DVD-Audio is a format for delivering high-fidelity audio content on a DVD. It offers many channels (from mono to 5.1 surround sound) at various sampling frequencies and sample rates. Compared to the CD format, the much higher capacity DVD format enables the inclusion of either considerably more music (with respect to total running time and quantity of songs) 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 or not the resulting audio enhancements are distinguishable to typical human ears. DVD-Audio currently forms a niche market, probably due to its dependency upon new and relatively expensive equipment.

Security

DVD-Audio discs employ a robust copy prevention mechanism, called Content Protection for Prerecorded Media supported by the DVD+RW Alliance (IBM, Intel, Matsushita, and Toshiba).

Unlike DVD-Video's CSS, as of 2005, CPPM has not yet been cracked.

All above formats are also available as 8 cm (3 inch) sized DVD mini discs (not mini-DVD, which describes DVD data on a CD) with a disc capacity of 1.5 GB.

Players and recorders

Modern DVD recorders often support additional formats, including DVD+/-R/RW, CD-R/RW, MP3, WMA, SVCD, JPEG, PNG, Scalable Vector Graphics, KAR and MPEG-4 (DivX/XviD). Some also include USB ports or flash memory readers. Many players are priced from under £50 and recorders from £200.

DVD drives for computers usually come with one of two kinds of Regional Playback Control (RPC), either RPC-1 or RPC-2; This is used to enforce the publisher's restrictions on what regions of the world the DVD can be played. See Regional lockout.

Competitors and successors

There are several possible successors to DVD being developed by different consortiums: Sony/Panasonic's Blu-ray Disc (BD), Toshiba's HD DVD, the Holographic Versatile Disc, and Maxell's holographic disc.

The first generation of holographic media with 300 GB of storage capacity and a 160 Mbit/s transfer rate is scheduled for release in late 2006 by Maxell and its partner, InPhase.

On November 18, 2003, the Chinese news agency Xinhua reported the final standard of the Chinese government-sponsored Enhanced Versatile Disc (EVD), and several patents for it. However, since then the format has generally failed to live up to expectations.

On November 19, 2003, the DVD Forum decided by a vote of eight to six that HD DVD will be its official HDTV successor to DVD. This had no effect on the competing Blu-ray Disc Association's (BDA) determination that its format would succeed DVD, especially since most of the voters belonged to both groups.

On April 15, 2004, in a co-op project with TOPPAN Printing Co., Sony successfully developed the paper disc, a storage medium that is made out of 51% paper and offers up to 25 GB of storage, about five times more than the standard 4.7 GB DVD. The disc can be easily cut with scissors and recycled, offering foolproof data security and an environment-friendly storage media.

As reported in a Summer 2005, issue of Popular Mechanics, it is not yet clear which technology will win the format war over DVD. HD DVD discs contain less information than Blu-ray discs (15GB vs. 25GB for single layer, 30GB vs. 50GB for dual layer), but Blu-ray requires changes in manufacturing machinery and techniques.

It is possible that neither Blu-ray, HD DVD, nor alternative next-generation optical recording products will succeed. The storage capacities of hard disk drives and solid-state memory have grown faster than those of optical discs (since CD's introduction year, 1983, storage capacity of HDDs grew by a factor of about 100,000, from 5 MB to 500 GB, while the capacitiy of Blu-ray is only 90 times larger than CD), and all three are much more capable of storing general consumer content —such as photos, music, and video— than in the past. Hard disk drives having a few terabytes of storage capacity will be on the market before 2008. A terabyte is equivalent to about 2000 CD-ROMs, 130 DVD-9s, or 20 dual-layer BDs. However, hard disk drives and memory cards are at the moment hundreds of times more expensive than optical discs (£30 or more compared to £0.30), so they will never replace discs as a publishing format. The price per gigabyte of a hard disk drive, £0.20 (£100/500GB), is lower than that of a recordable DVD-4.7, £0.32 (£1.50/4.7GB), or much lower than that of a two-layer DVD-8.5, £1.18(£10/8.5GB), and direct access to large amounts of information is much more convenient with a hard disk drive. As true broadband (25 Mbps or higher) becomes widely available in a decade or two, physical media will become less important.

The new generations of optical formats have restricted access (anti-copy mechanisms), and it is therefore possible that consumers will ignore them as they did with Super Audio CD.

Direct-to-DVD

The popularity of DVDs has caused the term "direct-to-DVD" to widely replace "Direct-to-video". However, the lucrative market for DVDs has resulted in less stigma for direct-to-DVD releases as compared to direct-to-video releases. Some minor films can be made with a small budget and turn a profit on DVD sales alone, and some are made specifically for this purpose.

See also

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