DVD is an optical storage media format that is used for playback of movies with high video and sound quality and for storing data. The abbreviation "DVD" originates from Digital Versatile Disc.
A DVD disc can be:
Unlike Compact discs, where sound is stored in a basically different way than data, a DVD disc should always contain the data in a common filesystem, in the UDF format.
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DVD-Video discs require a DVD-Video player, which is similar to a common VCR, but cannot normally record onto the discs as standard. Commercial DVD movies are encoded using a combination of MPEG-2 compressed video and Dolby AC-3 audio (often in multi-channel formats.) Typical data rates for DVD movies range from 3-10 Mbps, and the bitrate is usually adaptive.
The audio data on a DVD movie can be of the format PCM, DTS, MPEG audio, or Dolby Digital (AC-3). In countries using the NTSC standard any movie should contain a sound track in PCM or Dolby AC-3 format, 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.
Initially, in countries using the PAL standard (most of Europe) the sound of DVD was supposed to be standardised on PCM and MPEG-2 audio, 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.
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 jacks or TOSLINK, 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 systems typically include 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 in the form of component video, which fully separates the signal into its three components (whereas s-video has two, and composite only one). Not to leave well enough alone, the connectors are further confused by using a number of physical connectors, RCA or BNC, as well as using VGA cables in a non-standard way (VGA is normally RGB). Even worse, there are often two sets of component outputs, one carrying interlaced video, and the other progressive.
Given that an increasing number of TVs are essentially RGB monitors attached to an internal computer, it might seem odd that the video signal isn't sent in a digital format in the same way the sound is. This is particularly odd considering that even the component video system is not capable of being used at higher resolutions for high-definition television. In this case the reasons are legal as opposed to technological.
Most DVD-Video titles use Content Scrambling System (CSS) encryption, which is intended to discourage people from making perfect digital copies to another medium or from bypassing the region control mechanism (see below). Discs can also specify that the player use Macrovision, an analog anti-copying mechanism that prevents the consumer from copying the video onto a VCR tape. This alone would not prevent the duplication of DVD discs in their entirety without decrypting the data, given suitable equipment, although "consumer-grade" DVD writers deny this ability by refusing to duplicate the tracks on the disk which contain the decryption keys.
The CSS system has caused problems for the inclusion of DVD players in strictly open source operating systems, since open source player implementations can not officially obtain access to the decryption keys or license the patents involved in the CSS system. Proprietary software players may also be difficult to find on some platforms. However at least one 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 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.
DVD movies can contain a region code, denoting which area of the world it is targeted at, which is completely independent of encryption. The commercial DVD-video player specification dictates that players must only play discs that contain their region code. This allows the film studios to set different retail prices in different markets and extract the maximum possible price from consumers. With region coding, studios can dictate release schedules and prices around the world. However, many DVD players allow playback of any disc, or can be modified to do so (in the United States, this is a violation of the Digital Millennium Copyright Act).
|0||Playable in all regions|
|1||United States, Canada, and U.S. territories|
|2||Europe, Greenland, South Africa, Lesotho, Swaziland, Japan, Egypt, and the Middle East|
|3||Southeast Asia, South Korea, Hong Kong, Indonesia, Philippines, Taiwan|
|4||Australia, New Zealand, Mexico, Central America, South America,|
|5||Russia, other former Soviet Union countries, eastern Europe, Indian subcontinent, Mongolia, Africa|
|6||People's Republic of China|
|7||Reserved for future use|
|8||International venues such as airplanes, cruise ships, etc.|
Region 0 designates no actual region, but that a region 0 disc should play in all players. Region 0 players were created that would allow any region disc to be played in them, but studios responded by adjusting regioned discs to refuse to play if the player was determined 0 (since no player should anyway).
In the 1980s two incompatible video formats had been launched on the consumer market with VHS and Beta. This slowed the uptake of this technology as many consumers chose to wait to see which format would become the most popular. To order to avoid a repeat of this, all parties agreed on the new DVD format in December, 1995. By this stage the term Digital Versatile Disk was used by some companies to reflect the fact that non-video formats of the disk would also be used.
DVD-Audio is a new format to deliver high-fidelity audio content on a DVD. It offers stereo and surround sound capability, as well as a maximum of 4 hours of stereo audio per disc (2 hours of surround audio). The introduction of the DVD-Audio format angered many early-adopters and enthusiasts of the DVD format. With no modification it would have been possible to make a DVD-Video disc containing only audio in PCM or Dolby Digital, which would work perfectly in any DVD player. While the DVD-Audio discs do have higher fidelity, there is debate as to whether or not the difference is distinguishable to typical human ears. DVD-Audio currently forms a niche market, probably due to requiring new and rather expensive equipment.
See also : Nuon, DeCSS, Netflix (DVD rental), DivX, DIVX, and EZ-D.