Codecs
Codecs are compression schemes that reduce data storage requirements; both lossy and lossless compression techniques have been developed and are being used. Depending on the application, either can be used to greatly increase the amount of audio or video storable on fixed-bit-capacity media.
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 ISO MPEG-2, H.264/AVC, and SMPTE VC-1. MPEG-2 video allows decoder backward compatibility for DVDs. H.264, sometimes called MPEG-4 part 10 (but now mainly referred to as AVC), is a more recent video codec. VC-1 is another MPEG-4 derivative codec mostly developed by Microsoft (based on Microsoft's previous work in Windows Media 9). BD-ROM titles with video must store video using one of the three mandatory codecs (multiple codecs on a single title are allowed).
The initial version of Sony's Blu-ray Disc-authoring software shipped with support for only 1 video-codec: MPEG-2.[citation needed] Consequently, all launch titles were encoded in MPEG-2 video.[citation needed] A subsequent update allowed the content producers to author titles in any of the 3 supported codecs: MPEG-2, VC-1, or H.264.[citation needed] 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).[citation needed] 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.
For audio, BD-ROM players are required to support Dolby Digital AC-3, DTS, and Linear PCM (up to 7.1 channels). Dolby Digital Plus, and lossless formats Dolby TrueHD and DTS HD are player optional. BD-ROM titles must use one of mandatory schemes for the primary soundtrack (linear PCM, Dolby Digital, or DTS). A secondary audiotrack, if present, may use any of the mandatory or optional codecs.[48] If Dolby Digital Plus is used, it must be accompanied by an AC-3 soundtrack (which provides the "core" bitstream). For uncompressed PCM and lossless audio in Dolby TrueHD or DTS-HD Master Audio formats, Blu-ray Discs support encoding in up to 24-bit/192 kHz for a maximum of six channels, or up to eight channels with at most 24-bit/96 kHz sampling.[49]
For users recording digital television programming, the recordable Blu-ray Disc standard's datarate of 54 Mbit/s is more than adequate to record high-definition broadcasts from any source (IPTV, cable/satellite, or terrestrial). For Blu-ray Disc movies the maximum transfer rate is 48 Mbit/s (1.5x) (both audio and video payloads together), of which a maximum of 40 Mbit/s can be dedicated to video data. This compares favorably to the maximum of 36.55 Mbit/s in HD DVD movies for audio and video data.[50]
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 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
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 to the DVD region codes. Blu-ray players sold in a certain region should only be able to 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.
| Region code | Area[52] |
|---|---|
| A | North America, Central America, South America, Japan, Taiwan, North Korea, South Korea, Hong Kong, and Southeast Asia. |
| B | Europe, Greenland, French territories, Middle East, Africa, Australia, and New Zealand. |
| C | India, Bangladesh, Nepal, Mainland China, Pakistan, Russia, Central, and South Asia. |
This arrangement places the countries of the major Blu-ray manufacturers (Japan, Korea, Malaysia) in the same region as the U.S., thus ensuring early releases of U.S. content to those markets. Reportedly, early BD releases (including Casino Royale) are "ALL" region and therefore compatible in various BD players around the globe.
http://en.wikipedia.org/wiki/Blu-ray
No comments:
Post a Comment