DVD Demystified

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Chapter 4
48 kHz sampling frequency at no more than 16 bits per sample. The
recorder must watermark the copies (see following section) and keep track
of what copies have been made so that only one copy of original audio content
can be made per recorder unless otherwise authorized by the content
owner by setting CCI parameters for number of allowed copies. An ISRC
must be included with the content so that the recorder can track the number
of copies it makes of any title. The content owner also can specify
allowed sound quality for copies (CD-Audio, two-channel full-quality, multichannel
full-quality). Aside from analog and CD-quality digital audio
(IEC-958) outputs, all other outputs from a copy-protected DVD-Audio disc
must be encrypted by a method such as DTCP.
Watermarking Watermarking is a technical process of embedding information
into content in a way that is intended to be transparent to the user
of the content, yet which cannot be removed or altered easily. Each digital
video frame or segment of digital audio is permanently marked with noise
that is supposedly undetectable by human ears or eyes. (As discussed in
Chapter 2, there is much debate about how undetectable watermarking is
in practice. The amount of watermarking can be varied so that an especially
dynamic piece could have a lower level of watermarking to reduce its
impact.) The noise carries a digital signature that can be recognized by
recording and playback equipment. The signature stays connected to the
content regardless of digital or analog transformations. Watermarking does
not directly protect the content—it only identifies the status of the content.
When used with a content protection system, watermarking usually carries
CMI. When the content is played on compliant devices, they recognize the
CMI carried in the watermark and abide by its constraints. This only works
if a “hook” is present that compels devices to be compliant. Encryption is
the carrot to which watermarking is attached. To get the keys and secrets
needed to play encrypted content, manufacturers must sign a license, which
may require that watermark detection be implemented.
Another use of watermarking is to detect if an analog copy has been
made or if the content has been digitally reencoded. A fragile watermark, as
used by the Secure Digital Music Initiative (SDMI), is designed to be
destroyed by any processing of the content, thus indicating that it is not the
original version.
DVD-Audio uses watermarking technology developed by Verance. All
DVD-Audio players licensed to play CPPM or CPRM discs are required to
include circuitry to recognize the Verance watermark. Watermarking will
be added to DVD-Video at some point, as a requirement for new players
only. It will not make existing DVD-Video players obsolete.
DVD-Audio recorders include remarking encoders that change the