DVD-Audio
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DVD-Audio is a format for delivering high-fidelity audio content on a DVD. It offers many channels (from mono to 5.1 surround sound) at various sampling frequencies and sample rates. Compared to the CD format, the much higher capacity DVD format enables the inclusion of either considerably more music (with respect to total running time and quantity of songs) or far higher audio quality (reflected by higher linear sampling rates and higher vertical bit-rates, and/or additional channels for spatial sound reproduction).
Audio on a disc can be 16, 20 or 24 bit, with sampling rates of 44.1, 48, 88.2, 96, 176.4 or 192 kHz. (The highest sampling rates of 176.4 and 192 kHz are limited to stereo only.) Different sampling sizes and frequencies can be used on a single disc. Audio is stored on the disc in LPCM format or is losslessly compressed with Meridian Lossless Packing. The DVD-Audio player may downmix surround sound to stereo if the listener does not have a surround sound setup. DVD-Audio may also feature menus, still images, slideshows and video. Such discs commonly contain Dolby Digital or DTS versions of the audio (with lossy compression, usually downsampled to lower sampling sizes and frequencies) in the DVD-Video section. This is done to ensure compatibility with DVD-Video players.
The introduction of the DVD-Audio format angered many early adopters of the DVD format. While DVD-Audio discs are capable of higher fidelity sound than CDs, there is debate as to whether or not the difference is distinguishable to typical human ears. DVD-Audio currently forms a niche market, probably due to its dependency upon new and relatively expensive equipment. DVD-Audio is currently in a format war with SACD. DVD-Audio might find more success in the form of DualDisc and CD/DVD packages than as a standalone format.
Copy prevention
DVD-Audio discs employ a robust copy prevention mechanism, called Content Protection for Prerecorded Media (CPPM). CPPM, managed by the 4C Entity, prevents users from extracting audio to computers and portable media players.
Because DVD-Video's content-scrambling system (CSS) was quickly broken, DVD-Audio's developers sought a better method of blocking unauthorized duplications. They developed CPPM, which uses a media key block (MKB) to authenticate DVD-Audio players. In order to decrypt the audio, players must obtain a media key from the MKB, which also is encrypted. The player must use its own unique key to decrypt the MKB. If a DVD-Audio player's decryption key is compromised, that key can be rendered useless for decrypting future DVD-Audio discs. DVD-Audio discs also can utilize digital watermarking technology developed by the Verance Corporation.
As of 2005, CPPM has not been cracked.
The 4C Entity also developed a similar specification, Content Protection for Recordable Media (CPRM), which is used on Secure Digital Cards.
References
Labriola, Don. (August 25, 2003). Digital Content Protection, Part II (http://www.extremetech.com/article2/0,1558,1231582,00.asp). ExtremeTech.com
External links
- The 4C Entity LLC (http://www.4centity.com/) - licensors of the Content Protection for Prerecorded Media (CPPM) specificationaf:DVD-Oudio