[Matroska-devel] Re: Dirac Video Codec

Arioch /BDV/ the_Arioch at nm.ru
Tue Oct 5 13:47:40 CEST 2004


The stars so gaily glistened... (Tue, 05 Oct 2004 13:14:31 +0200 @510)
...while the fading voice of Steve whispered through the darkness:

 SL> EBML docs ? Where ? ;)
The link below :-P

 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 :-)

 SL>  but it's there. To understand EBML you also need to understand what 
 SL> global elements are, like Void and CRC-32. 

I know, but i don't know how to understand :-)

 ??>> met in different archivers. Some programs can show file info but will 
 ??>> not de-compress until password is given. 

 SL> That's up to the application, not the format.

Yes, that is just an ode to EBML flexibility :-)



 ??>> 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.

-- 
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http://Arioch.nm.ru/FL/Fidolook_SL.png    Mail: the_Arioch<at>nm<dot>ru


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