Blu-ray (2)

Technical specifications

Laser and optics

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.)

Hard-coating technology

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. Advances in polymer technology eventually made the cartridges unnecessary.

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.

Software standards

Codecs

Codecs are compression schemes that store audio and video more efficiently, either giving longer play time or higher quality per megabyte. There are both lossy and lossless compression techniques.

The BD-ROM specification mandates certain codec compatibilities for both hardware decoders (players) and the movie-software (content). For video, all players are required to support MPEG-2, H.264/AVC, and SMPTE VC-1. MPEG-2 is the codec used on regular DVDs, which allows backwards compatibility. H.264/AVC was developed by MPEG and VCEG as a modern successor of MPEG-4. VC-1 is another MPEG-4 derivative codec mostly developed by Microsoft. BD-ROM titles with video must store video using one of the three mandatory codecs. Multiple codecs on a single title are allowed.

The choice of codecs affects the producer's licensing/royalty costs, as well as the title's maximum runtime, due to differences in compression efficiency. Discs encoded in MPEG-2 video typically limit content producers to around two hours of high-definition content on a single-layer (25 GB) BD-ROM. The more advanced video codecs (VC-1 and H.264) typically achieve a video runtime twice that of MPEG-2, with comparable quality.

MPEG-2 was used by many studios, including Paramount Pictures (which initially used the VC-1 codec for HD DVD releases) for the first series of Blu-ray discs that were launched throughout 2006. Modern releases are now often encoded in either H.264/AVC or VC-1, allowing film studios to place all content on one disc, reducing costs and improving ease of use. Using these codecs will also free many GB of space for storage of bonus content in HD (1080i/p) as opposed to the SD (480i/p) typically used for most titles. Some studios (such as Warner Bros.) have released bonus content on discs encoded in a different codec than the main feature title; for example the Blu-ray release of Superman Returns uses VC-1 for the feature film and MPEG-2 for bonus content (presumably because it is simply ported from the DVD release).

For audio, BD-ROM players are required to support Dolby Digital AC-3, DTS, and linear PCM. Players may optionally support Dolby Digital Plus, and lossless formats Dolby TrueHD and DTS-HD Master Audio. BD-ROM titles must use one of the mandatory schemes for the primary soundtrack. A secondary audiotrack, if present, may use any of the mandatory or optional codecs.

For users recording digital television programming, the recordable Blu-ray Disc standard's initial data rate of 36 Mbit/s is more than adequate to record high-definition broadcasts from any source (IPTV, cable/satellite, or terrestrial). Blu-ray movies have a maximum data transfer rate of 54 Mbit/s, a maximum AV bitrate of 48 Mbit/s (for both audio and video data), and a maximum video bitrate of 40 Mbit/s. This compares to HD DVD movies which have a maximum data transfer rate of 36 Mbit/s, a maximum AV bitrate of 30.24 Mbit/s, and a maximum video bitrate of 29.4 Mbit/s.

Java software support

At the 2005 JavaOne trade show, it was announced that Sun Microsystems' Java cross-platform software environment would be included in all Blu-ray Disc players as a mandatory part of the standard. Java is used to implement interactive menus on Blu-ray Discs, as opposed to the method used on DVD video discs, which uses pre-rendered MPEG segments and selectable subtitle pictures, which is considerably more primitive and less seamless. Java creator James Gosling, at the conference, suggested that the inclusion of a Java Virtual Machine as well as network connectivity in some BD devices will allow updates to Blu-ray Discs via the Internet, adding content such as additional subtitle languages and promotional features that are not included on the disc at pressing time. This Java Version is called BD-J and is a subset of the Globally Executable MHP (GEM) standard. GEM is the world-wide version of the Multimedia Home Platform standard.

Region codes Regions for Blu-ray standard

A : Americas; East and Southeast Asia; U.S. territories; Bermuda.

B : Africa, Europe, Oceania; Middle East; Kingdom of the Netherlands; British overseas territories, French territories; Greenland.

C : Central and South Asia; Mongolia, Russia, and People's Republic of China.

Blu-ray Discs may be encoded with a region code, intended to restrict the area of the world in which they can be played, similar in principle to the DVD region codes, although the used geographical regions differ. Blu-ray Disc players sold in a certain region may only play discs encoded for that region. The purpose of this system is to allow motion picture studios to control the various aspects of a release (including content, date, and in particular price) according to the region. Discs may also be produced without region coding, so they can be played on all devices.
This places the countries of the major Blu-ray manufacturers (Japan, Korea, Malaysia) in the same region as North America. As of early 2008, about two-thirds of all released discs were region-free.

In the Blu-ray region coding system, the United States is placed in region A while regions B and C are used for countries which can experience localization delays before U.S. titles are officially released. The opposite, though, is sometimes true and a few new titles such as Harry Potter and the Goblet of Fire and Running Scared were released in certain European countries before the U.S. release. In response to the DVD region system, multi-region and region-free DVD players became dominant in certain markets; certain Blu-ray player models have been modified to allow for playback of Blu-ray discs from Regions A and B and DVD discs from Regions 1 and 2.

Digital rights management (DRM)

The Blu-ray Disc format employs several layers of digital rights management. AACS decryption process
Advanced Access Content System (AACS) is a standard for content distribution and digital rights management. It is developed by AS Licensing Administrator, LLC (AACS LA), a consortium that includes Disney, Intel, Microsoft, Matsushita (Panasonic), Warner Bros., IBM, Toshiba and Sony.

Since appearing in devices in 2006, several successful attacks have been made on the format. The first known attack relied on the trusted client problem. In addition, decryption keys have been extracted from a weakly protected player (WinDVD). However, even though some AACS cryptographic keys have been compromised, new releases will use new, uncompromised keys.

BD+ was developed by Cryptography Research Inc. and is based on their concept of Self-Protecting Digital Content.[50] BD+ is effectively a small virtual machine embedded in authorized players. It allows content providers to include executable programs on Blu-ray Discs. Such programs can:examine the host environment, to see if the player has been tampered with. Every licensed playback device manufacturer must provide the BD+ licensing authority with memory footprints that identify their devices.verify that the player's keys have not been changed.execute native code, possibly to patch an otherwise insecure system.transform the audio and video output. Parts of the content will not be viewable without letting the BD+-program unscramble it.

If a playback device manufacturer finds that its devices have been hacked, it can potentially release BD+-code that detects and circumvents the vulnerability. These programs can then be included in all new content releases.
The specifications of the BD+ virtual machine are available only to licensed device manufacturers. A list of licensed adopters is available from the BD+ website.

BD+ was made available for content publishers in June 2007. The first titles using BD+ were released in October the same year. Players from Samsung and LG had problems playing back those titles until the manufacturers updated their firmware, but this problem was later identified as being related to BD-Java use, not BD+.[52] BD+ protection was fully circumvented with the release 6.4.0.0 of AnyDVD HD program.

BD-ROM Mark is a small amount of cryptographical data that is stored physically differently from normal Blu-ray Disc data. Bit-by-bit copies that do not replicate the BD-ROM Mark are impossible to decode. A specially licensed piece of hardware is required to insert the ROM-mark into the media during replication. Through licensing of the special hardware element, the BDA believes that it can eliminate the possibility of mass producing BD-ROMs without authorization.