Blu-ray Disc
Blu-ray Discs (BD), the successor to DVDs. As the name suggests, Blu-ray uses a blue or violet laser beam with a wavelength of 405 nm and a numerical aperture of 0.85. This reduces the diameter of the scanning beam in comparison to the red laser system of the DVD and significantly increases storage capacity. In addition, an increase in the rotational speed achieves a scanning rate of 36 Mbit/s (with 1X drive speed). With a diameter of 120 mm and thickness of 1.2 mm, Blu-ray Discs have the same dimensions as DVDs. There is a difference, however, in the internal structure: Whereas DVDs consist of two 0.6 mm-thick disc halves enclosing a recording layer, Blu-ray Discs are constructed of a single disc, with the data located under a 0.1 mm-thick protective layer consisting of a transparent lacquer that protects against scratches. This results in a storage capacity of 25 GB with one data layer, and up to 50 GB with two layers.
Three video compression codecs have been specified for Blu-ray Discs:
- MPEG-2 HL@MP (a high-definition variation of the MPEG 2 codecs, which is used on DVDs)
- AVC (MPEG-4), a newer type of encoder that achieves identical quality at a lower transmission rate
- VC-1 (the SMPTE’s standardized version of Microsoft’s Windows Media 9)
The file structure on the disc is UDF 2.5.
The following audio formats have been specified for Blu-ray Discs:
- LPCM
- Dolby Digital
- Dolby Digital Plus
- Dolby TrueHD / MLP Lossless
- DTS digital surround
- DTS HD
There are two interactive application layers for Blu-ray Discs: HDMV (high definition movie mode) and BD-J (Blue-ray Disc Java).HDMV offers expanded interactivity in comparison to traditional DVD video—for example, the ability to jump to the next picture in a slide show without interrupting the background music.BD-J, which is programmed in a variant of Java, makes it possible to integrate a large number of interactive applications such as interactive films, fade-ins and fade-outs, games, web offerings and additional multimedia information.There are all kinds of creative possibilities of how to use this programming language.
Copy Protection:
AACS (Advanced Access Content System) is the result of a collaborative effort by major film studios, manufacturers of consumer electronics, and the IT industry. The founders of this initiative include, among others, Disney, Sony, Microsoft, IBM, Intel, Panasonic, Toshiba and Warner Brothers. The Blu-ray Disc format contains solutions for digital delivery and for user access to stored content.
AACS is the successor to the CSS system used with DVDs. It was very comprehensively expanded and revised in order to ensure stable protection of contents in this new generation of storage media.
In addition to protecting against illegal copying, AACS makes it possible to transfer disc contents to devices, such as conforming home media servers, that assure further legal use of the contents. AACS can be installed in stand-alone, networked, and/or portable devices, to protect the contents from unauthorized digital or analog copying.
The content owner makes the processed data available to licensed disc replicators. During the authoring, this data must be appropriately prepared for the subsequent encryption process. On request, the AACS licensing organization then provides the replicator with key files and contents certificates that prevent unauthorized copying. Downscaling is also possible, however, so that only standard definition signals are provided in the player’s analog outputs, for example.
The replicator then manufactures the required number of discs with the appropriate copy protection and delivers them to the customer.
The AACS organization, for its part, delivers corresponding keys to the manufacturers of players; these keys then make it possible for legally produced Blu-ray Discs to be played on the player.
Two additional protection systems are also in effect in Blu-ray Discs: BD+ and the BD ROM mark.
BD+ is a executable program that is stored on Blu-ray Discs. Working in the background, this program checks whether the video and audio stream is being manipulated. If this is the case, playback is stopped.
The BD ROM Mark is an invisible mark on the disc that cannot be forged. This identifying mark can only be produced by manufacturers that have been authorized and equipped to do so by the Blu-ray Disc Association (BDA). This measure is intended to combat mass production piracy.
» Blu-ray specifications for input data
» Blu-ray specifications for offset printing
