[Gllug] CD's and Computers

[Mike Brodbelt]

On Wed, 2002-04-10 at 16:46, t.clarke wrote:
> Interesting notes earlier about deliberately writing invalid CRC's on the discs.
> 
> I wonder if that invalidates whatever agreements the record companies made with
> Philips in respect of the 'red book' (or whatever)  standard. I would assume
> that the agreement to use the Philips patents (or have they expired?) included
> an undertaking to stick to the standard, which would include the CRC usage.

It does. Philips have been making unhappy noises about these copy
protection schemes, and have threatened to prevent companies emplying
the from using the Compact Disc logo. The patents haven't expired yet,
but don't have long left to run.
 
> Hopefully, if this sort of fiddling around becomes more prevalent, computer
> CD drive manufacturers will simply incorporate the same logic as domestic
> players (which from recollection goes something along the lines of 'if you
> can't reconstruct the correct data from the interleaved reed-solomon code
> then interpolate the data from the preceding/following data blocks').

I've heard there are already some manufacturers advertising that their
drives "read past" bogus CRC's. Doubtless this wil become more prevalent
if the protection scheme becomes more widespread, in the same way that
modified DVD players remove macrovision protection from video
recordings.

Mike.



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