DVD-Audio Copy Framework: The Devilish Details
The International Media Manufacturing Magazine, ""One To One"", reports the following on the ""DVD-Audio Copy Framework."" The agreement by Warner, BMG, EMI, Sony and Universal Music to support the copy protection framework hammered out by the Copy Protection Working Group (CPTWG) has helped move the DVD-Audio standard one step closer to reality. Now the full details of the copy protection framework are emerging, showing that the options draw fairly clearly from the ideas used both on DVD-Video and CD-ROM and previous copy management systems such as SCMS. ""Weíve spent a year working together on this,"" notes Alan Bell, a key mover in the CPTWG. ""Itís fundamentally a deal with the content owners about the framework that should be used."" What the CPTWG has done is present a single out-line framework that details what the content protection should be achieving, rather than try and decide exactly what technology should be used to implement the various options. The framework defines several types of protection and copy control options, which can be implemented individually or together. There is no compulsion to use any of the schemes, and some publishers may well decide for various reasons - technical or otherwise - that they want to produce DVD-Audio discs in exactly the same way as CD discs - universally playable with straightforward PCM audio. Whilst all the options go a stage or two further than DVD-Videoís control and protection technology, there is one thing noticeably absent from the framework. The audio disc per se does not include Region Coding, although this may be implemented if the disc is a Universal (DVD-Audio/Video) disc which carries with it full DVD-Video options. Like DVD-Video, the framework relies on the concept of ""Participating"" systems, in other words players and digital recorders or writers all have to include DVD content control electronics to be able to handle the disc. The system, whether itís a physical hardware player or software on a PC, will be able to decode the encryption and detect information hidden in the audio stream as a watermark. Other copy control information (CCI) is also extracted either from the disc or the watermark and acted on by the player or passed on to the recorder. So when copy controlled music is digitally copied, the end result should also end up encrypted and carrying the correct CCI. Information now released by the Copy Protection Technical Working Group (CPTWG), fully details the principles that will be applied to DVD-Audioís content control and protection. The three key elements of copy protection for DVD-Audio are Encryption, Data Hiding (Data Watermarking) and Content Control Information instructions. Encryption The music content will be encrypted using a system similar to the CSS used for DVD-Video. There are some new subtle additions to the encryption scheme, which takes advantage of the further developments in copy protection since the introduction of CSS. Increased efficiency and a more advanced key technology are likely to be introduced so that the system can use a number of different keys, protecting it from wholesale access, should a particular key be cracked by hackers. ""CSS for DVD-Video is based on a single secret,"" notes Alan Bell of the CPTWG,"" and content owners have said that it is now a couple of years on and we can do better. Whilst the system is comparable to CSS, there will be a multiplicity of keys, so if one player has cracked then all future discs can exclude that player."" Introducing encryption for the audio is aimed as an integral part of the overall copy control scheme for the new generation of digital players and recorders, whilst also barring direct digital copying to what the CPTWG call legacy systems ñ older digital recorders such as CD-R and DAT. Universal Access The record industry has always conceded that a wholesale block on all copying would be counter-productive and alienate a vast number of the CD-buying population. So within the framework there is a minimum access arrangement that will apply to all DVD-Audio discs, no matter how heavily the content owners want to apply copy control. All users will be able to take at least 1 digital stereo copy from the DVD-Audio disc. The disc will allow access to PCM resolutions up to 48kHz. However, there will be no automatic right to record either multichannel sound or bit rates higher than 48kHz. ""These copies will be unencrypted, but will still contain copy control data hidden in the watermark."" A by-product of this access arrangement is that the record industry can continue to pursue legislation to introduce, or continue, surcharges on blank media as recompense for home copying. Copy Control Options The additional features of the DVD-Audioís copy control are centered on four CCI parameters that define what can be copied, how and how many times. These parameters will be built into the data stream, rather than being simple flags on the disc as with SCMS, and will control the recorder, telling it what can, and canít, be copied. ""The parameters are carried with the key in the same package. There will also be a small set in the watermark as an option,"" explains Bell. DVD-Audio Copy Control Information Copy Permission Parameter (C) The permission parameter specifies the number of copies that can be made, with a default value of 1. This also requires and ISRC entry to be stored by the recorder, to track the number of copies made. The copy can be flagged as ""no more copies,"" to prevent serial copying. Sound Quality Parameter (Q) This sets the upper quality level that copies can be made in, and supports three specific values: -Stereo/CD quality. This is the default value. -Stereo/Full quality. Allows stereo recording at all sampling rates on the disc. -Multichannel/Full quality. Allows recording of all music content ñ stereo or multichannel - and at any sampling rate. Related Content Parameter (R) Since the DVD-Audio disc can contain other material such as text and pictures, which may have separate licensing arrangements, there is a separate copy control for the additional content. These are separate to the normal copy permission parameters so different settings can be made for audio and additional content. Transactional Parameter (T) This is a new feature for any DVD format, adding the capability of conditional access to parts of the disc. The transactional parameter is almost Divx by the backdoor, allowing the authorizations to be altered depending on a transaction by the customer, which could involve payment for further copy permissions.