[Matroska-devel] Re: Dirac Video Codec
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
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.
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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