• What is Blu-ray?
• Blu-ray Specs

What is Blu-ray?

Commonly called a BD disc, Blu-ray is one new of the new optical disc formats for the next generation. Predominantly for High Definition viewing and containing large amounts of data, Blu-ray was designed in a joint venture by world leaders in electronics, computers and media manufacturers  with companies including Apple, Dell, Hitachi, HP, JVC, LG, Mitsubishi, Panasonic, Pioneer, Philips, Samsung, Sharp, Sony, TDK and Thomson.

As the name implies, Blu-ray uses a blue-violet laser (405nm) instead of relying on the red laser technology found to be used on DVDs and CDs. To enable Blu-ray discs to hold a larger capacity (single layer 25GB, dual layer 50gb) the wavelength of the laser is much shorter to that of red laser (650nm), thus allowing data to be packed more tightly on the disc even though the disc size is the same as a DVD/CD.

Types of Blu-ray discs

BD-ROM - read-only format for distribution of HD movies, games, software, etc.
BD-R - recordable format for HD video recording and PC data storage.
BD-RE - rewritable format for HD video recording and PC data storage.

Average amount of video storage

Over 9 hours of high-definition (HD) video on a 50GB disc.

About 23 hours of standard-definition (SD) video on a 50GB disc.

Video codec’s supported by Blu-ray

MPEG-2 - enhanced for HD, also used for playback of DVDs and HDTV recordings.

MPEG-4 AVC - part of the MPEG-4 standard also known as H.264 (High Profile and Main Profile).

SMPTE VC-1 - standard based on Microsoft's Windows Media Video (WMV) technology.

Audio codec’s supported by Blu-ray

Linear PCM (LPCM) - offers up to 8 channels of uncompressed audio.

Dolby Digital (DD) - format used for DVDs also known as AC3, offers 5.1-channel surround sound.

Dolby Digital Plus (DD+) - extension of DD, offers increased bitrates and 7.1-channel surround sound.

Dolby TrueHD - extension of MLP Lossless, offers lossless encoding of up to 8 channels of audio.

DTS Digital Surround - format used for DVDs, offers 5.1-channel surround sound.

DTS-HD - extension of DTS, offers increased bitrates and up to 8 channels of audio.

Access restriction technology

Commercialized HD DVDs integrate content protection technology specified by AACS LA (Advanced Access Content System License Administrator). The Advanced Access Content System (AACS) is a standard for content distribution and digital rights management, which will allow restricting access to and copying of the next generation of optical discs and DVDs.

The group developing it includes Disney, Intel, Microsoft, Matsushita (Panasonic), Warner Brothers, IBM, Toshiba, and Sony. The standard has been adopted as the access restriction scheme for HD DVD and Blu-ray Disc.
The proposal is based on broadcast encryption using Naor-Naor-Lotspiech subset difference trees. The proposal was voted one of the technologies most likely to fail by IEEE Spectrum magazine. Concerns about the approach include its similarity to past systems that failed, such as Content Scrambling System (CSS), and the inability to preserve security against attacks that compromise large numbers of players.

System overview

AACS utilizes cryptography to control the use of digital media. AACS-protected content is encrypted under one or more title keys using the Advanced Encryption Standard (AES). Title keys are derived from a combination of a media key and several elements, including the volume ID of the media (e.g., a physical serial number embedded on a DVD), and a cryptographic hash of the title usage rules.
The principal difference between AACS and earlier content management systems such as CSS is in the means by which title-specific decryption keys are distributed. Under CSS, all players of a given model are provisioned with the same, shared decryption key. Content is encrypted under the title-specific key, which is itself encrypted under each model's key. In CSS, each volume contains a collection of several hundred encrypted keys, one for each licensed player model. In principle, this approach allows licensors to "revoke" a given player model (prevent it from playing back future content) by omitting the encryption key corresponding to that model. In practice, however, revoking all players of a particular model is costly, as it causes many users to lose playback capability. Furthermore, the inclusion of a shared key across many players makes key compromise significantly more likely, as was demonstrated by a number of compromises in the mid-1990s.

The approach of AACS provisions each individual player with a unique set of decryption keys which are used in a broadcast encryption scheme. This approach allows licensors to "revoke" individual players, or more specifically, the decryption keys associated with the player. Thus, if a given player's keys are compromised by an attacker, the AACS licensing authority can simply revoke those keys in future content, making the keys/player useless for decrypting new titles.

Mandatory managed copy

This feature will enable consumers to make legal copies of their Blu-ray movies that can be transferred over a home network. Please note that "mandatory" refers to the movies having to offer this capability, while it will be up to each hardware manufacturer to decide if they want to support this feature. An internet connection will also be required to authorize managed copies of Blu-ray movies that can be transferred over a home network.

Internet connectivity

While an internet connection is not necessary for normal playback of Blu-ray movies, having one will be needed for value-added features such as downloading new extras and subtitles that were not included at the time of pressing, watching recent movie trailers, web browsing, etc.

Interactivity

As well as being able to access features using an internet connection, BD-J (the script adopted for Blu-ray programming based on a high end level of java) allows many new possibilities for menus and special features. For example, you will be able to bring up the menu system as an overlay without stopping the movie. Picture in Picture will be supported so you could have the director of the movie on the screen explaining the shooting of a scene while the scene is playing in the background.

Playstation 3

With the launch of the PS3 in November 2006, Blu-ray offers gamers and movie watchers an all-in one High Definition home entertainment experience as well as being backward compatible with previous PS2 games, PSOne games and standard DVDs. The PS3 also allows users access to previous saved games from the PS2.

The PS3’s standard resolution for the system is 1080p (1920x1080 progressive, not interlaced). 1080i, 720p, 480p and 480i are also supported.

Outputs will include composite, S-Video and component via AV cables, but for the best image quality the 60GB version of the system also employs a built-in HDMI connection. For in-games Dolby Digital 5.1, Dolby Pro Logic II and DTS are all supported and will be outputted via optical and analogue stereo connections.

Compatibility

While it is not compulsory for manufacturers, the Blu-ray Disc Association recommends that Blu-ray drives should be capable of reading DVDs for backward compatibility. For instance, Samsung's first Blu-ray drive (now available) will read and write CD, DVD, and Blu-ray.

Reference: Blu-ray.com Wikipedia.com IGN.com