Physical Format
Variations and sizes
A single-layer Blu-ray disc (BD) has enough storage capacity (25GB) for approximately two hours of high-definition video with audio. A dual-layer (50GB) BD can hold enough data for approximately four hours of HD video. TDK recently announced that they have created a working Blu-ray disc capable of holding 200GB of data (six 33GB data layers).
Laser and optics
Blu-ray systems use a blue-violet laser operating at a wavelength of 405 nm, similar to the one used for HD DVD, to read and write data. Conventional DVDs and CDs use red and 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, using a higher numerical aperture (0.85, compared with 0.6 for DVD, and 0.65 for HD DVD), higher quality, dual-lens system, and making the cover layer over the data level thinner (0.1mm (Blu-ray) vs 0.6mm (HD DVD)) to avoid undesirable optical effects, the laser beam can be focused much more tightly. This produces a smaller spot on the disc than in existing CDs or DVDs, and allows more information to be physically stored in the same area.
Hard-coating technology
Because the Blu-ray standard places data so close to the surface of the disc, early discs were susceptible to dust and scratches and had to be enclosed in plastic caddies for protection. Such an inconvenience, the consortium worried, would retard Blu-ray's adoption in the face of the rival HD DVD standard; HD DVDs place data further away like DVDs. CDs use a single layer of lacquer over the reflective data backing (on the label side) and are more susceptible to damage on the label side than DVDs, HD DVDs, or Blu-ray Discs.
A solution was announced in January 2004 with the introduction of a clear polymer coating that gives Blu-ray Discs unprecedented scratch resistance. The coating was developed by TDK Corporation and is called "Durabis". It allows BDs to be cleaned safely with only a tissue. The coating is said to successfully resist "wire-wool scrubbing" according to Samsung Optical technical manager Chas Kalsi. HD DVDs are more similar to current CDs and DVDs in this respect, as they can be manufactured using essentially the same processes and do not require such a surface layer.
Software Standards
Codecs
The codecs used to encode video and audio largely determine the amount of space needed to store the content on the disc. Some or all of the initial movies released in Blu-ray format will use MPEG-2.
A compliant BD-ROM player must be able to decode at least the following codecs: MPEG-2, the standard used for DVDs; MPEG-4's H.264/AVC codec; and VC-1, a codec based on Microsoft's Windows Media 9. Realistically, when using MPEG-2, quality considerations would limit the publisher to around two hours of high-definition content on a single-layer BD-ROM. The two more advanced video codecs can typically attain four hours of high quality video.
For audio, BD-ROM supports up to 7.1 channel surround sound using the linear (uncompressed) PCM, Dolby Digital and DTS formats also used on DVDs. In addition, it also supports Dolby Digital Plus and the lossless formats Dolby TrueHD and DTS HD. The linear PCM 5.1, Dolby Digital 5.1 and DTS 5.1 formats are mandatory, meaning that one of them may be used as the sole soundtrack on a disc, because every player will have a decoder that can process any of these three bitstreams. For lossless audio in movies in the PCM, Dolby TrueHD or DTS-HD formats, Blu-ray discs support encoding in up to 24-bit/192kHz for up to six channels, or up to eight channels of up to 24-bit/96kHz encoding. For reference, even new big-budget Hollywood films are mastered in only 24-bit/48kHz, with 16-bit/48kHz being common for ordinary films.
For users recording digital television broadcasts, the Blu-ray's baseline datarate of 36 Mbit/s will be more than adequate to record high-definition signals. Support for new codecs will evolve as they are encapsulated by broadcasters into their MPEG-2 transport streams, and consumer set-top boxes capable of decoding them are rolled out.
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 players as a mandatory part of the standard. Java will be 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. Java creator James Gosling, at the conference, suggested that the inclusion of a Java virtual machine as well as network connectivity in 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 will be called BD-J and will be a subset of the Globally Executable MHP (GEM) standard. GEM is the world-wide version of the Multimedia Home Platform standard.
Digital rights management
Blu-ray has an experimental digital rights management (DRM) feature called BD+ which allows for dynamically-changing keys for the cryptographic protections involved. Should the keys currently in use be 'cracked', manufacturers can update them and build them into all subsequent disks, preventing a single key discovery from permanently breaking the entire scheme. Blu-ray also mandates the Mandatory Managed Copy system, which allows users to copy content a limited number of times, but requiring registration with the content provider to acquire the keys needed; this feature was originally requested by HP]. The lack of a dynamic encryption model is what has made DeCSS a disaster from the industry's perspective: once CSS was cracked, all DVDs from then on were open to unauthorized decryption (commonly known as "ripping"). However this new technology, together with Self-Protecting Digital Content (SPDC), can allow players judged 'bad' to be effectively disabled, preventing their use by their purchaser or subsequent owners.
The Blu-ray Disc Association also agreed to add digital watermarking technology to the discs. Under the name "ROM-Mark", this technology will be built into all ROM-producing devices, and prevent content from being reproduced in the event that a watermark is detected. Through licensing, the BDA believes that it can eliminate the possibility of mass producing BD-ROMs without authorization.
In addition, Blu-ray players must follow AACS guidelines pertaining to outputs over non-encrypted interfaces. This is set by a flag called the Image Constraint Token (ICT), which restricts the output-resolution without HDCP to 960×540. The decision to set the flag to restrict output ("down-convert") is left up to the content provider. According to CED Magazine, Sony/MGM and Disney currently have no plans to down-convert, and Fox is opposed to it as well. Warner Pictures is a proponent of the ICT, and it is expected that Paramount will also implement it. Other studios releasing Blu-ray content have not yet commented on whether or not they will use down-conversion. AACS guidelines require that any title that implements the ICT must clearly state so on the packaging.
Applications
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 avaliable) will read and write CD, DVD, and Blu-ray.
JVC has developed a three layer technology that allows putting both standard-definition DVD data and HD data on a BD/DVD combo disc. If successfully commercialized, this would enable the consumer to purchase a disc which could be played on current DVD players, and reveal its HD version when played on a new BD player.
Stand-alone recorders and games consoles
The first Blu-ray recorder was unveiled by Sony on March 3, 2003, and was introduced to the Japanese market in April that year. On September 1, 2003, JVC and Samsung Electronics announced Blu-ray based products at IFA in Berlin, Germany. Both indicated that their products would be on the market in 2005.
Sony has announced that the PlayStation 3 will be shipped with a 2x Blu-ray drive, likely read-only as for most game console optical drives. According to Sony's press releases, it will support DVD(8x), CD(24x) and SACD (2x) formats in addition to BD-ROM, BD-R, and BD-RE. The Japanese release date for PS3 is on November 11, 2006. The release date of the PS3 everywhere else has been announced for November 17, 2006.
Microsoft, who did not include Blu-ray technology in its Xbox 360 console, has stated that it is possible that they could add a Blu-ray drive to the unit. However, further comments from Microsoft state that they have no plans to do so, and were merely just trying to illustrate the flexibility of the Xbox 360. In February 2006 (3 months after the console's release), Microsoft announced the development of an external HD DVD drive for use with the Xbox 360, opposing Sony's new Blu-ray format. Microsoft has since said that if Blu-ray becomes the more dominant format, it may release a Blu-ray drive add-on.
PC data storage
Originally, blu-ray drives in production could only transfer approximately 36 Mbit/s (54 Mbit/s require for BD-ROM), but 2x speed drives with a 72 Mbit/s transfer rate are now avaliable. Rates of 8x or more are planned for the future.
Hewlett Packard has announced plans to sell Blu-ray-equipped desktop PCs and laptops. In December 2005, HP announced that they would also be supporting the rival HD DVD technology. Philips was scheduled to debut a Blu-ray computer drive in the second half of 2005, but it was also delayed. On March 10, 2005 Apple Computer joined the Blu-ray Disc Association.
In July 2005, information was leaked about an upcoming Pioneer Blu-ray drive; the OEM BDR 101A. On December 27, 2005, Pioneer formally announced the drive which was released in the late second quarter of 2006. The drive writes at 2x on BD-R and BD-RE, 8x on DVD+R and DVD-R, and 4x on DVD-RW and DVD+RW.
Optical heads allowing the reading of CD/DVD/Blu-ray discs have already been developed and are expected to be included after first release of DVD/Blu-ray only drives.
The Panasonic Blu-ray SW-5582 is the first drive to support all 3 formats.
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