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DVD(dvd)DVD is an optical disc storage media format that isused for playback of movies with high video and sound quality and for storing data. A DVD disc is similar in appearance to a compact disc .
HistoryDuring the early 1990s there were two high density optical storage standards indevelopment; one was the Multimedia Compact Disc (MMCD) backed by Philips and Sony , and the other was the Super Disc (SD) supported by 8 major consumer electronics giants including Toshiba and Time-Warner . IBM led an effort to unite the various companies behind a single standard, anticipating a repeat of the costly formatwar between VHS and Betamax in the 1980s . The result was the DVD format, announced in September of 1995 . The official DVD specification was released in Version 1.0 in September , 1996 . It is maintained by the DVD Forum , formerly the DVD Consortium, consisting of the ten founding companies and over 220 additional members.The first DVD players and discs were available in November of 1996 in Japan and in March of 1997 in the United States . "DVD" was originally an acronym for "digital versatile disc";some members of the DVD Forum believe that it should stand for "digital video disc", due to the fact that mostmembers of the public believe that DVD does stand for that. Toshiba , which maintainsthe official DVD Forum site, adheres to the interpretation of "digital versatile disc." The DVD Forum never reached a consensuson the matter, however, and so today the official name of the format is simply "DVD"; the letters do not 'officially' stand foranything. Technical informationA DVD can contain:
The disc medium can be:
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 disccapacity:
The capacity of a DVD-ROM can be visually determined by noting the number of data sides, and looking at the data side(s) ofthe disc. Double-layered sides are usually gold-colored, while single-layered sides are silver-colored, like a CD . Each medium can contain any of the above content and can be any layer type (double layer DVD-R and DVD+R are announced for 2004 ). The DVD Forum has created the official DVD-R(W) standards. But as thelicensing cost for this technology is very high, another group was founded: the DVD plus RW Alliance who created the DVD+R(W) standard with lower licensing costs. Even so, DVD+R(W)media are typically more expensive then DVD-R(W) media. The "+" (plus) and "-" (dash) are two similar technical standards that are partially compatible. As of 2004 , both formats are equally popular, with about half of the industry supporting "+", and the other half "-".It is open to debate whether either format will push the other out of the market, or whether they will co-exist indefinitely. AllDVD readers are supposed to read both formats (though real-world compatibility lies around 90% for both formats), and mostcurrent DVD writers can write both formats. Unlike compact discs, where sound ( CDDA , Red Book ) is stored in a fundamentallydifferent fashion than data ( Yellowbook et al.), a properly authored DVD disc will always contain data in the UDF filesystem. The speed of a DVD drive is given in multiples of 1350 kB/s, which means that a drive with speed 16x allows a data transferrate of 16 x 1350 = 21600 kB/s (21.09 MB/s). DVD-VideoDVD-Video discs require a DVD-drive with a MPEG-2 decoder (eg. a DVD-player or a DVD computer drive with asoftware 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 moviesrange from 3-10 Mbit/s, and the bitrate is usually adaptive. The audio data on a DVD movie can be of the format PCM , DTS , MPEG audio, or DolbyDigital (AC-3). In countries using the NTSC standard any movie shouldcontain a sound track in PCM or Dolby AC-3 format, and any NTSC player must support these two, all the others are optional. Thisensures 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 wassupposed to be standardized 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 DolbyAC-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 besomewhat frustrating. Most systems include an optional digital connector for this task, which is then paired with a similar inputon 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 theaudio equipment. When playing compact discs, the signal is sent in S/PDIF formatinstead. 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 appearin the form of component video , which fully separates the signal intoits three components (whereas s-video has two, and composite only one). Additionally, the connectors are further confused byusing 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 areoften two sets of component outputs, one carrying interlaced video ,and the other progressive. In Europe, SCART connectors are typically used, which offer areasonable compromise between video quality, which is comparable and frequently superior to S-Video , and cost. DVD Video may also include subtitles in various languages. They are stored as images with transparent background. DVD Video may contain Chapters for easy navigation (and continuation of a partially watched film). A major selling point of DVD Video is that its storage capacity allows for a wide variety of extra features in addition to thefeature film itself. This can include audio commentary that is timed to the film sequence, documentary features, unused footage, trivia text commentary, games and film shorts. SecurityMost DVD-Video titles use Content ScramblingSystem (CSS) encryption, which is intended to discourage people from making perfect digital copies to another medium or frombypassing 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 withoutdecrypting the data, given suitable equipment, although "consumer-grade" DVD writers deny this ability by refusing to duplicatethe tracks on the disc 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 thedecryption keys or license the patents involved in the CSS system. Proprietary software players may also be difficult to find on someplatforms. However at least one successful effort has been made to write a decoder by reverse engineering , resulting in DeCSS . This has led tolong-running legal battles and the arrest of some of those involved in creating or distributing the DeCSS code, through the useof the U.S. Digital MillenniumCopyright Act , on the grounds that such software could also be used to facilitate unauthorized copying of the data on thediscs. Region codesDVD movies can contain a region code, denoting which area of the world it is targeted at, which is completely independent ofencryption. The commercial DVD-video player specification dictates that players must only play discs that contain their regioncode. This allows the film studios to set different retail prices in different markets and extract the maximum possible pricefrom consumers. With region coding, studios can dictate release schedules and prices around the world. However, many DVD playersallow playback of any disc, or can be modified to do so. Region coding pertains to regional lockout , which originated from the video game industry.
European Region 2 DVDs may be sub-coded D1 through D4. "D1" identifies a UK-only release. "D2" and "D3" identify European DVDsthat are not sold in the UK and the Republic of Ireland. "D4" identifies DVDs that are distributed throughout Europe. Region 0 designates no actual region, but it is used as shorthand for a disc meant to be playable on all players. On such adisc, the actual region coding is R1/2/3/4/5/6. In the early days, region 0 players were created that would allow any region discto be played in them, but studios responded by adjusting regioned discs to refuse to play if the player was determined 0 (sinceno player should anyway). This system is known as Regional Coding Enhancement or just RCE. Many view region code enforcement as a violation of WTO free trade agreements; however, no legal rulings have yet been made in thisarea. However, many manufacturers of DVD players now freely supply information on how to disable the region code checking, and onsome recent models, it appears to be disabled by default. DVD-AudioDVD-Audio is a new format to deliver high-fidelity audio content on a DVD. It offers many channels (from mono to 5.1 surroundsound ) at various sampling frequencies and sample sizes. Audio on a disc can be 16, 20, or 24 bit and can be at samplingrates of 44.1, 48, 88.2, 96, 176.4, or 192 kHz (the highest sampling rates of 176.4 and 192 kHz are limited to stereo only). Inaddition, different sampling sizes and frequencies can be used on a single disc. Audio is stored on the disc in LPCM format or is losslessly compressed with Meridian Lossless Packing . The DVD-Audio player may downmix surround sound to stereo if thelistener does not have surround sound. DVD-Audio may also feature menus, still images, slideshows, and video. Also, DVD-Audiodiscs usually contain Dolby Digital or DTS versions of the audio ( lossy compressed , usually downsampled to lower sampling sizesand frequencies) in the DVD-Video section. This is done to ensure compatibility with DVD-Video players. The introduction of the DVD-Audio format angered many early-adopters of the DVD format. While the DVD-Audio discs do havehigher fidelity, there is debate as to whether or not the difference is distinguishable to typical human ears. DVD-Audiocurrently forms a niche market, probably due to requiring new and rather expensive equipment. DVD-Audio is currently (as of 2003 ) in a format war with SACD . Most market observers believe the winner of the war will eventually supplant the CompactDisc due to its superior playback compabilities, unless a new and superior format takes over from either. DVD types
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. Competitors and successorsThere are two successors to DVD being developed by two different consortiums: The Blu-ray Disc and the Advanced OpticalDisc . On November 18 , 2003 , the Chinesenews agency Xinhua reports the final standard of the Chinese government-sponsored Enhanced Versatile Disc (EVD) and several patentsaround it. On November 19 , 2003 the DVD Forumdecided with eight to six votes that the Advanced OpticalDisc is the HDTV successor of the DVD. See also
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ddv, disc, dv, discs, dd, data, vdd, gb, vd, player, , rw This article is completely or partly from Wikipedia - The Free Online Encyclopedia. Original Article. The text on this site is made available under the terms of the GNU Free Documentation Licence. We take no responsibility for the content, accuracy and use of this article. Anoca.org Encyclopedia 0.04s |
