DVD
From ECDL.web
DVD is an optical disc storage media format, invented and developed by Philips, Sony, Toshiba, and Time Warner in 1995. DVD discs offer higher storage capacity than compact discs while having the same dimensions.
The official DVD charter documents specify that the basis of the DVD name stems from the term "digital versatile disc". Usage in the present day varies, with Digital Versatile Disc, Digital Video Disc, and DVD being the most common.
DVD was adopted by movie and home entertainment distributors to replace the ubiquitous VHS tape as the primary means of distributing films to consumers in the home entertainment marketplace. DVD was chosen for its superior ability to reproduce moving pictures and sound, for its superior durability, and for its interactivity. Interactivity had proven to be a feature which consumers, especially collectors, favored when the movie studios had released their films on laser disk. When the price point for a laser disk at approximately $100 per disk moved to $20 per disk at retail, this luxury feature became available for mass consumption. Simultaneously the movie studios decided to change their home entertainment release model from a rental model to a for purchase model. This allowed all fans to become collectors and pushed the movie DVD into a demand position that essentially made it the most successful consumer product of all time. DVD as a format had two qualities at the time that were not available in any other interactive medium: 1. Enough capacity and speed to provide high quality, full motion video and sound, and 2. low cost delivery mechanism provided by consumer products retailers who quickly moved to sell their players for under $200 and eventually for under $50 at retail. In addition, the medium itself was small enough and light enough to mail using general first class postage. Almost over night, this created a new business opportunity and model for business innovators like Netflix to re-invent the home entertainment distribution model.
[edit] Capacity
The basic types of DVD (12 cm diameter, single-sided or homogeneous double-sided) are referred to by a rough approximation of their capacity in gigabytes. The 12 cm type is a standard DVD, and the 8 cm variety is known as a MiniDVD. These are the same sizes as a standard CD and a mini-CD, respectively.
- DVD-1: single-sided, single-layer, 8 cm, 1.46 GB
- DVD-2: single-sided, dual-layer, 8 cm, 2.66 GB
- DVD-3: dual-sided, single-layer, 8 cm, 2.92 GB
- DVD-4: dual-sided, dual-layer, 8 cm, 5.32 GB
- DVD-5: single-sided, single-layer, 12 cm, 4.70 GB
- DVD-9: single-sided, dual-layer, 12 cm, 8.54 GB
- DVD-10: dual-sided, single-layer, 12 cm, 9.40 GB
- DVD-14: dual-sided, single/dual-layer, 12 cm, 13.24 GB
- DVD-18: dual-sided, dual-layer, 12 cm, 17.08 GB
[edit] Technology
DVD uses 650 nm wavelength laser diode light as opposed to 780 nm for CD. This permits a smaller pit to be etched on the media surface compared to CDs (0.74 µm for DVD versus 1.6 µm for CD), allowing in part for a DVD's increased storage capacity. In comparison, Blu-ray disc, the successor to the DVD format, uses a wavelength of 405 nm, and one dual-layer disc has a 50 GB storage capacity.
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 semitransparent layer. In some DVD players, the layer change can exhibit a noticeable pause, up to several seconds.
[edit] DVD recordable and rewritable
DVD recordables are now also used for consumer audio and video recording. Three formats were developed: DVD-R/RW, DVD+R/RW (plus), and DVD-RAM. DVD-R is available in two formats, General (650 nm) and Authoring (635 nm), where Authoring discs may be recorded with encrypted content but General discs may not.
Although most DVD writers can nowadays write the DVD+R/RW and DVD-R/RW formats (usually denoted by "DVD±RW" and/or the existence of both the DVD Forum logo and the DVD+RW Alliance logo), the "plus" and the "dash" formats use different writing specifications. Most DVD readers and players will play both kinds of discs, although older models can have trouble with the "plus" variants.
Dual-layer recording allows DVD-R and DVD+R discs to store significantly more data—up to 8.54 gigabytes per disc, compared with 4.7 gigabytes for single-layer discs. DVD recordable discs supporting this technology are backward-compatible with some existing DVD players and DVD-ROM drives. Many current DVD recorders support dual-layer technology, and the price is now comparable to that of single-layer drives, although the blank media remain more expensive. The recording speeds reached by dual-layer media are still well below those of single-layer media.
[edit] DVD-Video
DVD-Video is a consumer video format used to store digital video on DVD discs, and is currently the dominant consumer video format. The format went on sale in Japan on November 1, 1996, in the United States on March 1, 1997, in Europe on October 1, 1998 and in Australia on February 1, 1999. DVD-Video became the dominant form of home video distribution in Japan when it first went on sale in 1996, but did not become the dominant form of home video distribution in the United States until June 15, 2003, when weekly DVD-Video in the United States rentals began outnumbering weekly VHS cassette rentals, reflecting the rapid adoption rate of the technology in the U.S. marketplace. Currently, DVD-Video is the dominant form of home video distribution worldwide, although in Japan it was surpassed by Blu-ray Disc when Blu-ray first went on sale in Japan on March 31, 2006.
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).
[edit] DVD region code
DVD region codes are a copyright protection technique designed to allow motion picture studios to control aspects of a release, including content, release date, and price, according to the region. DVD video discs may be encoded with a region code restricting the area of the world in which they can be played.
| Region code | Area |
|---|---|
| 0 | Informal term meaning "worldwide". Region 0 is not an official setting; discs that bear the region 0 symbol either have no flag set or have region 1–6 flags set. |
| 1 | United States, Canada, Bermuda, U.S. territories |
| 2 | Europe (except Russia, Ukraine, and Belarus), Middle East, Egypt, Japan, South Africa, Swaziland, Lesotho, Greenland |
| 3 | Southeast Asia, South Korea, Republic of China (Taiwan), Hong Kong, Macau |
| 4 | Mexico, Central America, South America, Australia, New Zealand, Oceania |
| 5 | India, Afghanistan, Ukraine, Belarus, Russia, Africa (except Egypt, South Africa, Swaziland and Lesotho), Central and South Asia, Mongolia, North Korea |
| 6 | China, Hong Kong |
| 7 | Reserved for future use |
| 8 | International venues such as aircraft, cruise ships, etc. |
| ALL | Region ALL discs have all 8 flags set, allowing the disc to be played in any locale on any player. |
DVDs sold in the Baltic States use both region 2 and 5 codes. DVDs sold in Japan use the region 2 code, while Macau and Taiwan use the region 3 code. Hong Kong has historically used Region 3 and has added region 6 since the reunification, now using both.
Region 0 (playable in all regions except 7 and 8) is widely used by China and the Philippines. DVDs in Latin America uses both the region 1 and region 4 codes. Most DVDs in India combine the region 2, region 4, and region 5 codes; Indian Disney discs contain only the region 3 code.
European region 2 DVDs may be sub-coded "D1" to "D4". "D1" are United Kingdom–only releases; "D2" and "D3" are not sold in the UK and Ireland; "D4" 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. So-called "Region 0" and "ALL" discs are meant to be playable worldwide.
The term "Region 0" also describes the DVD players designed or modified to incorporate Regions 1–6, thereby providing compatibility with most discs, regardless of region.
[edit] 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 5.1 surround sound) at various sampling frequencies. 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 sampling rates and greater sample resolution, 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.
[edit] Use as backup medium
Durability of DVDs is measured by how long the data may be read from the disc, assuming compatible devices exist that can read it: that is, how long the disc can be stored until data is lost. Five factors affect durability: sealing method, reflective layer, organic dye makeup, where it was manufactured, and storage practices. The longevity of the ability to read from a DVD+R or DVD-R is largely dependent on manufacturing quality, ranging from 2 to 15 years, and is believed to be an unreliable medium for backup unless great care is taken for storage conditions and handling. Manufacturers claim life spans ranging from 30 to 100 years for DVD, DVD-R and DVD+R discs, and up to 30 years for DVD-RW, DVD+RW and DVD-RAM.
[edit] Improvements and succession
In 2006, two new formats called HD DVD and Blu-ray Disc were released as the successor to DVD. HD DVD competed unsuccessfully with Blu-ray Disc in the format war of 2006–2008. A dual layer HD DVD can store up to 30GB and a dual layer Blu-ray disc can hold up to 50GB. However, unlike previous format changes, e.g., audio tape to compact disc or VHS videotape to DVD, there is no immediate indication that production of the standard DVD will gradually wind down, as they still dominate, with around 87% of video sales and approximately one billion DVD player sales worldwide. In fact experts claim that the DVD will remain the dominant medium for at least another five years as Blu-ray technology is still in its introductory phase.
The Holographic Versatile Disc (HVD) is an optical disc technology that may one day hold up to 6 terabytes (TB) of information, although the current maximum is 500GB. It employs a technique known as collinear holography.
The 5D DVD, being developed in the Swinburne University of Technology in Melbourne, Australia, uses a multilaser system to encode and read data on multiple layers. Disc capacities are estimated at up to 10 terabytes, and the technology could be commercially ready within ten years.