What is HD-DVD?
HD DVD stands for High Definition Digital Versatile Discs. HD DVD is one of the two competing next-generation optical disc formats in the market today. HD DVD is less costly to manufacture than Blu-Ray discs because its main manufacturing requirements are similar to the one for DVDs and it can be produced easily without any major changes in the manufacturing line. This translates to lower costs of production and lower costs for the end-users.
HD-DVD was developed by Toshiba and Hitachi.
Disc Formats
There will be three formats for HD DVD. The first one, HD DVD read-only memory discs or HD DVD ROM will be used for movies, music, games and software. HD DVD-R or HD DVD recordable, on the other hand, is a one-time-write disc format capable of recording HDTV data and any other computer files. HD DVD rewritable is basically the same as the recordable version. It is different only because of the fact that you can rewrite or record on top of the previous data.
Storage Capacity
HD DVD discs will have far greater capacities than the old DVDs but less than Blu-Ray. A single layer of HD DVD is capable of storing as much as 15GB of data while dual layered HD DVD discs will have a capacity of 30GB. Triple layered HD DVD discs are still being researched and developed.
HD DVD Disc
HD DVD actually uses a different technology from the old DVD when it comes to reading and sorting the data. HD DVDs use the same blue laser technology that Blu-Ray technology uses in order to store more data. The aperture in the optical pick up head used in HD DVD players are however smaller by 0.2 than Blu-Ray's 0.85 aperture. The difference in aperture size is because of the differences in disc thickness (HD DVD and DVD 0.6mm, Blu-ray 0.1mm), surface layer and the resulting laser effectiveness because of optical effects.
HD-DVD uses a 405nm wavelength blue-violet laser and an 0.65nm pickup aperture. HD-DVD's are coated with a 0.6mm protective surface layer, which is the same thickness used in DVD's.
HD DVD Security Features
For security, HD-DVD supports mandatory HDCP encrypted output, volume identifiers and Advanced Access Content System (AACS).
AACS LA, which is supported by pro Blu-Ray and HD DVD Technologies, will provide protection for both the HD DVDs and BDs. This security system is similar to the DVDs CSS which proved not to be effective in the case of protecting copyright contents for DVDs. AACS is however different to CSS because with AACS every player will have its own key to be used for broadcast encryption as opposed to having every player model assigned the same decryption keys. This new security system will enable licensors to tag individual units that leaked the security keys. As with Blu-Ray, HD DVDs will also have digital watermarking as an additional copyright protection feature to prevent unauthorized reproduction or duplication of media.
HD DVD Supported File Formats
The same compression formats for Blu-Ray Discs will also be compatible with HD DVDs. MPEG-4 AVC, MPEG-2 and MPEG-2 TS and VC-1 will be used to record HDTV data without compromising picture and audio quality with a data transfer rate of 36.55 Mbps. As with Blu-ray, HD DVDs will also be backwards compatible with existing codecs for DVD and CD.
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