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In this article:
- What are Blu-ray Discs
- Physical Attributes of Blu-ray Discs
- Software standards of Blu-ray Discs
What are Blu-ray Discs
Blu-ray Disc or BD is a next-generation optical disc format designed for high-density storage of data, most prominently, video. The Blu-ray standard has been develpoed by a group of consumer electronics and computer companies known as the Blu-ray Disc Association (BDA) which is led by Sony. Its major competitor is the HD DVD format for being the next generation optical standard.
The name Blu-ray is comes from the color of the laser used to read and write the data on these discs which is blue-violet. A Blu-ray Disc has higher storage capacity as compared to that of the current format of Digital Versatile Disc (DVD). This is attributable to the use of a shorter wavelength of 405 nm of the blue-violet laser allowing more data to be stored in the same space. This is significantly lower than the red laser used by DVDs which has a wavelength of 650 nm. It is capable of storing 25 Gigabytes of data in each layer.
Physical Attributes of a Blu-Ray Disc
- Variations and sizes
There are various types of blu-ray discs available, each with its own storage capacity. While a single-layer Blu-ray disc can store nearly 25GB (which is equal to around 2 hours of high-definition video with audio), a dual-layer Blu-ray disc can store 50GB of data, that is, around 4 hours of such video with audio. Recently, a 200GB Blu-ray disc has been developed by TDK.
- Laser and optics
As explained, a Blu-ray system uses a blue-violet laser with a wavelength of 405 nm to read and write data. This laser, when combined with a proper lens to focus on the disc space, is capable of storing way more data in the same space than other formats such as DVDs and CDs. This lens has an numerical aperture of .85 and a dual-lens system is used to prevent any unwanted optical effects.
- Hard-coating technology
The data stored on a Blu-ray disc is placed very, very close to the disc surface. This makes it easy for these discs to be damaged easily by external sources such as dust and scratches etc. Though initially they were covered in plastic caddies, the fear of losing it to the HD DVD format in the competition led to further developments and now Blu-ray discs have a layer of lacquer on the label side of the disc.
Software standards in Blu-ray Discs
- Codecs
It is planned that the initial movies to be released on Blu-ray discs would use the MPEG-2 format for encoding. It has been decided that a BD player must play atleast 4 of the many video standards which are MPEG-2, the DVD standard, H.264/AVC codec (by MPEG-4) and the VC-1 codec.
While MPEG-2 will allow no more than 2 hours of high-definition content on a disc, the other codecs usually allow around 4 hours of such content on a single disc. However, there is a significantly higher quality loss when the other codecs are used.
On the Audio front, BD-ROM or a Blu-ray disc can support up to 7.1 channel surround sound and formats that include PCM, Dolby Digital and DTS formats, same as on DVDs. Other formats supported are Dolby Digital Plus, Dolby TrueHD and DTS HD. The first three are to be necessarily supported to enable every player to be able to play them as all players are to include decoders for the three.
- Java Software Support
The Blu-ray discs are to include the Java environment as a part of the standard. Java would be used to implement the menus and subtitles in the disc. It is propsed that Java Virtual Machine also be included and so also network connectivity be enabled in all BD players. This would allow addition of more content such as subtitles in some other language which was not part of the original distribution. This JAVA package is to be called BD-J.
- Region Codes
There are three region codes on the Blu-ray discs. These are:
- A, for North America, South America, East Asia excluding China
- B, Europe and Africa
- And C, for China, Russia and other countries
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