[Matroska-devel] CodecState and CueCodecState

John Cannon spyder482 at gmail.com
Sun Jan 14 00:44:04 CET 2007


Hey,

I know it's been a LONG time since I've popped my head in here. :)

The original reasoning behind removing the sequence headers was to put them
in the codec state elements.  Since they didn't exist we just never bothered
with them.  In my mind, it shouldn't matter if the headers do remain in the
stream since they are part of the data the decoder expects.  However,
removing them entirely obviously creates playback issues.

John

On 1/13/07, Moritz Bunkus <moritz at bunkus.org> wrote:
>
> Hey,
>
> Mike (Haali) pointed out to me that keeping the sequence headers in the
> bitstream for MPEG-1/-2 video poses a problem when seeking. He proposed
> that we switch to using CodecState which has been created for just such
> a case.
>
> Now I started working on it and noticed a couple of things.
>
> 1. KaxCodecState does not exist yet in libmatroska. I've added it and
>    will commit the code soon.
>
> 2. CodecState is a child of BlockGroup. However, the specs don't say
>    clearly when exactly CodecState is supposed to take effect. I propose
>    that it must be processed by the codec _before_ the data in the same
>    BlockGroup is processed, even if the Block element is located before
>    the CodecState element in the same BlockGroup.
>
> 3. CueCodecState is supposed to point to a CodecState element. However,
>    the CodecState element itself does not contain a track number it
>    applies to; only the Block in the same BlockGroup does. I propose to
>    change the spec so that CueCodecState points to the _BlockGroup_
>    containing this CodecState element. Otherwise the demuxer would have
>    to do some real, real bad seeking backwards in order to find the
>    BlockGroup.
>
> Comments?
>
> Mosu
>
> --
> If Darl McBride was in charge, he'd probably make marriage
> unconstitutional too, since clearly it de-emphasizes the commercial
> nature of normal human interaction, and probably is a major impediment
> to the commercial growth of prostitution. - Linus Torvalds
>
>
>
>
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>


-- 
John Cannon
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