VCD , DVD ,HD DVD and Blu-Ray Disc (II)

HD DVD

HD DVD or High-Definition/Density Digital Versatile Disc is an obsolete high-density optical disc format for storing data and high-definition video. HD DVD was designed principally by Toshiba, and was envisaged to be the successor to the standard DVD format. However, in February 2008, Toshiba abandoned the format, announcing it would no longer develop or manufacture HD DVD players or drives.

HD DVD is derived from the same underlying technologies as DVD. Since all variants except the 3× DVD employed a blue laser with a shorter wavelength, it can store about 3¼ times as much data per layer as its predecessor (maximum capacity: 15 GB per layer instead of 4.7 GB per layer).

Much like the VHS vs .Betamax format war during the late 1970s and early 1980s, HD DVD was in a "format war" with rival format Blu-ray Disc to determine which of the two formats would become the leading carrier for high-definition content to consumers. In 2008, major content manufacturers and key retailers began withdrawing their support for the format. Toshiba's withdrawal from the format ended the high definition optical disc format war, effectively making rival Blu-ray Disc the dominant format for high definition video discs. The HD DVD Promotion Group was dissolved on 28 March 2008.

In the mid 1990s, commercial HDTV sets started to enter a larger market. However, there was no cheap way to record or play back HD content. There was no cheap storage medium that could store that amount of data, except JVC's Digital VHS and Sony's HDCAM. However, it was well known that using lasers with shorter wavelengths would yield optical storage with higher density. When Shuji Nakamura invented practical blue laser diodes, it was a sensation, although a lengthy patent lawsuit delayed commercial introduction.

The current specifications for HD DVD-ROM and HD DVD-RW are version 1.0. The specification for HD DVD-R is currently at 1.0; the HD DVD-RAM specification was never finalized.

HD DVD-ROM, HD DVD-R and HD DVD-RW have a single-layer capacity of 15 GB, and a dual-layer capacity of 30 GB. HD DVD-RAM has a single-layer capacity of 20 GB. Like the original DVD format, the data layer of an HD DVD is 0.6 mm below the surface to physically protect the data layer from damage. The numerical aperture of the optical pick-up head is 0.65, compared with 0.6 for DVD. All HD DVD players are backward compatible with DVD and CD

As with previous optical disc formats, HD DVD supports several file systems, such as ISO 9660 and Universal Disk Format (UDF). Currently all HD DVD titles use UDF version 2.5 as the file system.

Audio

HD DVDs support encoding in up to 24-bit/192 kHz for two channels, or up to eight channels of up to 24-bit/96 kHz encoding.

All HD DVD players are required to decode linear (uncompressed) PCM, Dolby Digital AC-3, Dolby Digital EX, DTS, Dolby Digital Plus and Dolby TrueHD. A secondary soundtrack, if present, can be stored in any of the aforementioned formats, or in one of the HD DVD optional codecs: DTS-HD High Resolution Audio and DTS-HD Master Audio.

For the highest-fidelity audio experience, HD DVD offers content-producers the choice of linear PCM, Dolby TrueHD and DTS-HD Master Audio. Due to the high-bandwidth requirements of linear-PCM, lossless audio on HD DVD movies has thus far been delivered in the lossless format Dolby TrueHD.

Video

HD DVD video can be encoded using VC-1, AVC, or MPEG-2. A wide variety of resolutions are supported, from low-resolution CIF, all SDTV resolutions supported by DVD-Video, and of course the HDTV formats: 720p, 1080i, and 1080p. All studio-released movie titles have featured video in a 1080-line format, with companion supplements in 480i or 480p. The vast majority of releases were encoded with VC-1, and most of the remaining titles encoded with AVC.

Blu-ray Disc

Blu-ray Disc (also known as Blu-ray or BD) is an optical disc storage medium. Its main uses are high-definition video and data storage. The disc has the same physical dimensions as standard DVDs and CDs.

The name Blu-ray Disc is derived from the blue laser (violet-colored) used to read and write this type of disc. Because of the beam's shorter wavelength (405 nanometres), substantially more data can be stored on a Blu-ray Disc than on the DVD format, which uses a red (650 nm) laser. A two-layer Blu-ray Disc can store 50 gigabytes, almost six times the capacity of a two-layer DVD, or ten times that of a single-layer DVD.

During the format war over high-definition optical discs, Blu-ray Disc competed with the HD DVD format. On February 19, 2008, Toshiba—the main company supporting HD DVD—announced that it would no longer develop, manufacture, and market HD DVD players and recorders, leading almost all other HD DVD companies to follow suit, effectively ending the format war.

Blu-ray Disc was developed by the Blu-ray Disc Association, a group representing makers of consumer electronics, computer hardware, and motion pictures. As of October 21, 2008, more than 970 Blu-ray Disc titles have been released in the United States and more than 500 Blu-ray Disc titles have been released in Japan.There are expected to be over 1300 Blu-ray Disc titles released in the United States by the end of 2008.

In 1998, commercial HDTV sets began to appear in the consumer market; however, there was no commonly accepted, inexpensive way to record or play HD content. In fact, there was no medium with the storage required to accommodate HD codecs, except JVC's Digital VHS and Sony's HDCAM. Nevertheless, it was well known that using lasers with shorter wavelengths would enable optical storage with higher density. When Shuji Nakamura invented practical blue laser diodes, it was a sensation, although a lengthy patent lawsuit delayed commercial introduction.

Philips and Sony started two projects applying the new diodes: UDO (Ultra Density Optical) and DVR Blue (together with Pioneer), a format of rewritable discs which would eventually become Blu-ray Disc (more specifically, BD-RE). The core technologies of the formats are essentially similar.

The first DVR Blue prototypes were unveiled at the CEATEC exhibition in October 2000. Because the Blu-ray Disc standard places the data recording layer close to the surface of the disc, early discs were susceptible to contamination and scratches and had to be enclosed in plastic cartridges for protection. In February 2002, the project was officially announced as Blu-ray, and the Blu-ray Disc Association was founded by the nine initial members.

The first consumer devices were in stores on April 10, 2003. This device was the Sony BDZ-S77; a BD-RE recorder that was made available only in Japan. The recommended price was US$3800; however, there was no standard for pre-recorded video and no movies were released for this player. The Blu-ray Disc standard was still years away as a newer, more secure DRM system was needed before Hollywood studios would accept it, not wanting to repeat the failure of the Content Scramble System used on DVDs.

The Blu-ray Disc physical specifications were finished in 2004. In January 2005, TDK announced that they had developed a hard coating polymer for Blu-ray Discs. The cartridges, no longer necessary, were scrapped. The BD-ROM specifications were finalized in early 2006. AACS LA, a consortium founded in 2004, had been developing the DRM platform that could be used to securely distribute movies to consumers. However, the final AACS standard was delayed, and then delayed again when an important member of the Blu-ray Disc group voiced concerns. At the request of the initial hardware manufacturers, including Toshiba, Pioneer and Samsung, an interim standard was published which did not include some features, like managed copy.

Blu-ray Disc uses a "blue" (technically violet) laser operating at a wavelength of 405 nm to read and write data. Conventional DVDs and CDs use red and near infrared lasers at 650 nm and 780 nm respectively.

The blue-violet laser's shorter wavelength makes it possible to store more information on a 12 cm CD/DVD sized disc. The minimum "spot size" on which a laser can be focused is limited by diffraction, and depends on the wavelength of the light and the numerical aperture of the lens used to focus it. By decreasing the wavelength, increasing the numerical aperture from 0.60 to 0.85 and making the cover layer thinner to avoid unwanted optical effects, the laser beam can be focused to a smaller spot. This allows more information to be stored in the same area. For Blu-ray Disc, the spot size is 580 nm. In addition to the optical improvements, Blu-ray Discs feature improvements in data encoding that further increase the capacity. (See Compact Disc for information on optical discs' physical structure.)

Because the Blu-ray Disc data layer is closer to the surface of the disc, compared to the DVD standard, it was at first more vulnerable to scratches. The first discs were housed in cartridges for protection.

TDK was the first company to develop a working scratch protection coating for Blu-ray Discs. It was named Durabis. In addition, both Sony and Panasonic's replication methods include proprietary hard-coat technologies. Sony's rewritable media are spin-coated with a scratch-resistant and antistatic coating. Verbatim's recordable and rewritable Blu-ray Disc discs use their own proprietary hard-coat technology called ScratchGuard.

Data and source mostly taken from Wikipedia.