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In computing and optical disc recording technologies, an optical disc (OD) is a flat, usually circular disc which encodes binary data (bits) in the form of pits and lands on a special material on one of its flat surfaces. The encoding material sits atop a thicker substrate which makes up the bulk of the disc and forms a dust defocusing layer. The encoding pattern follows a continuous, spiral path covering the entire disc surface and extending from the innermost track to the outermost track. The data is stored on the disc with a laser or stamping machine, and can be accessed when the data path is illuminated with a laser diode in an optical disc drive which spins the disc at speeds of about 200 to 4,000 RPM or more, depending on the drive type, disc format, and the distance of the read head from the center of the disc. Most optical discs exhibit a characteristic iridescence as a result of the diffraction grating formed by its grooves. This side of the disc contains the actual data and is typically coated with a transparent material, usually lacquer. The reverse side of an optical disc usually has a printed label, sometimes made of paper but often printed or stamped onto the disc itself. Unlike the 31⁄2-inch floppy disk, most optical discs do not have an integrated protective casing and are therefore susceptible to data transfer problems due to scratches, fingerprints, and other environmental problems.
Versatile Multilayer Disc is a high-capacity red-laser optical disc technology designed by New Medium Enterprises, Inc.. VMD was intended to compete with the blue-laser Blu-ray Disc format and had an initial capacity of up to 30GB per side.
The Blu-ray Disc Association (BDA) is the industry consortium that develops and licenses Blu-ray Disc technology and is responsible for establishing format standards and promoting business opportunities for Blu-ray Disc. The BDA is divided into three levels of membership: the Board of Directors, Contributors, and General Members.
The Holographic Versatile Disc (HVD) is an optical disc technology developed between April 2004 and mid-2008 that can store up to several terabytes of data on an optical disc 10 cm or 12 cm in diameter. The reduced radius reduces cost and materials used. It employs a technique known as collinear holography, whereby a green and red laser beam are collimated in a single beam. The green laser reads data encoded as laser interference fringes from a holographic layer near the top of the disc. A red laser is used as the reference beam to read servoinformation from a regular CD-style aluminium layer near the bottom. Servoinformation is used to monitor the position of the read head over the disc, similar to the head, track, and sector information on a conventional hard disk drive. On a CD or DVD this servoinformation is interspersed among the data. A dichroic mirror layer between the holographic data and the servo data reflects the green laser while letting the red laser pass through. This prevents interference from refraction of the green laser off the servo data pits and is an advance over past holographic storage media, which either experienced too much interference, or lacked the servo data entirely, making them incompatible with current CD and DVD drive technology.
Professional Disc (PFD) is a digital recording optical disc format introduced by Sony in 2003 primarily for XDCAM, its tapeless camcorder system. It was one of the first optical formats to utilize a blue laser, which allowed for a higher density of data to be stored on optical media compared to infrared laser technology used in the CD and red laser technology used in the DVD format.
Forward Versatile Disc (FVD) is an offshoot of DVD developed in Taiwan jointly by the Advanced Optical Storage Research Alliance (AOSRA) and the Industrial Technology Research Institute (ITRI) as a less expensive alternative for high-definition content. The disc is similar in structure to a DVD, in that pit length is the same and a red laser is used to read it, but the track width has been shortened slightly to allow the disc to have 5.4 GB of storage per layer as opposed to 4.7 GB for a standard DVD. The specification allows up to three layers for total of 15 GB in storage. WMV9 is used as the video codec allowing for 135 minutes of 720p video on a dual layer disc and 135 minutes of 1080i video on a three-layer disc. FVD uses AACS copy protection which is one of the schemes used in both HD DVD and Blu-ray Discs.
Dolby TrueHD is a lossless multi-channel audio codec developed by Dolby Laboratories which is used in home-entertainment equipment such as Blu-ray Disc players and A/V receivers. It is one of the successors to the Dolby Digital (AC-3) surround sound codec, which is used as the audio standard for the DVD-Video format. In this application, Dolby TrueHD competes with DTS-HD Master Audio, a lossless codec from DTS.
The first attempt at producing pre-recorded HDTV media was a scarce Japanese analog MUSE-encoded laser disc which is no longer produced.
This article compares the technical specifications of multiple high-definition formats, including HD DVD and Blu-ray Disc; two mutually incompatible, high-definition optical disc formats that, beginning in 2006, attempted to improve upon and eventually replace the DVD standard. The two formats remained in a format war until February 19, 2008, when Toshiba, HD DVD's creator, announced plans to cease development, manufacturing and marketing of HD DVD players and recorders.
DVD is a digital optical disc storage format invented and developed in 1995. The medium can store any kind of digital data and is widely used for software and other computer files as well as video programs watched using DVD players. DVDs offer higher storage capacity than compact discs while having the same dimensions.
Blu-ray or Blu-ray Disc (BD) is a digital optical disc data storage format. It was designed to supersede the DVD format, and is capable of storing several hours of video in high-definition. The main application of Blu-ray is as a medium for video material such as feature films and for the physical distribution of video games for the PlayStation 3, PlayStation 4, and Xbox One. The name "Blu-ray" refers to the blue laser used to read the disc, which allows information to be stored at a greater density than is possible with the longer-wavelength red laser used for DVDs.
HD DVD is an obsolete high-density optical disc format for storing data and playback of high-definition video. Supported principally by Toshiba, HD DVD was envisioned to be the successor to the standard DVD format.
China Blue High-Definition is a high definition optical disc format announced in September 2007 by the Optical Memory National Engineering Research Center (OMNERC) of Tsinghua University in China.
The high-definition optical disc format war was between the Blu-ray and HD DVD optical disc standards for storing high-definition video and audio; it took place between 2006 and 2008 and was won by Blu-ray Disc.
M2TS is a filename extension used for the Blu-ray Disc Audio-Video (BDAV) MPEG-2 Transport Stream (M2TS) container file format. It is used for multiplexing audio, video and other streams. It is based on the MPEG-2 transport stream container. This container format is commonly used for high definition video on Blu-ray Disc and AVCHD.
DVD-Video is a consumer video format used to store digital video on DVD discs. DVD-Video was the dominant consumer home video format in Asia, North America, Europe, and Australia in the 2000s until it was supplanted by the high-definition Blu-ray Disc. Discs using the DVD-Video specification require a DVD drive and an MPEG-2 decoder. Commercial DVD movies are encoded using a combination MPEG-2 compressed video and audio of varying formats. Typically, the data rate for DVD movies ranges from 3 Mbit/s to 9.5 Mbit/s, and the bit rate is usually adaptive. DVD-Video was first available in Japan on November 1, 1996, followed by a release on March 24, 1997 in the United States - to line up with the 69th Academy Awards that same day.
References
- Lawler, Richard (February 2, 2009). "HD NVD is China's home grown answer to Blu-ray, but does it have a chance?". Engadget .
- "China's proprietary red-ray NVD makes its debut". People's Daily Online. January 23, 2009.
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