[Matroska-devel] Re: Dirac Video Codec

Steve Lhomme steve.lhomme at free.fr
Tue Oct 5 14:04:11 CEST 2004


Arioch /BDV/ a écrit :

>  SL> Actually the CRC-32 is a feature of EBML, not just Matroska.
>  SL> It may not be crystal clear,
> 
> The least to say :-)
> It is even hightlighted (lowlighted?) - it is almost impossible to tell why and how w/o referensing to existing libraries and MKV files, that are too large to be good example :-)

Well, we haven't had any complaint about that so far. What exactly do 
you not understand about the CRC in Matroska ?

>  ??>> I just thought that good EBML library, would have some callbacks or
>  ??>> some gates to master application, so application would provide decoder
>  ??>> (here - password-using decrypter) and thus will generate derived EBML 
>  ??>> sub-stream.
> 
>  SL> Yes, we actually need something like that in Matroska too. I would 
>  SL> really like to have a good DRM solution in Matroska. And that implies 
>  SL> encrypting some parts of the stream.
> 
>  SL> That's somehow what is done in the (unused yet) Signature system you
>  SL> can see in the EBML specs.
> 
> Hmm, disagree.
> Signature does not imply any stream transformation, so parser just throuws Signature to the application, maybe starts internal signature checker - if it contains one, and go on parsing, cause the stream itself was not changed.
> 
> Parser does _not_ use application to recover part of the stream.
> Even would there be no application at all (say, some dumb EBML explorer or EBML-to-XML translator) it does not matter, cause EBML sub-stream is in its natural way.
> Quite the opposite thing if sub-stream is encrypted and parser _needs_ to use part of master-application.
> Then there is question how to do it effeciently and without context loss.

OK, my point was that it's almost like the signature. In the sense that 
encrypting some parts of a file would probably need the same kind of 
elements.

BTW it makes me think about signing the subjective elements of a tag, or 
maybe even encrypting them. This way only you and your pals could know 
your subjective comments/ratings about some music... It would be nice to 
allow that, and even better with the special-sub-element I was talking 
about.



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