[FFmpeg-devel] [PATCH] matroskaenc: add codec_tag lists back.

[Michael Niedermayer]

On Thu, Jan 24, 2013 at 11:20:58AM +0000, Carl Eugen Hoyos wrote:
> Paul B Mahol <onemda <at> gmail.com> writes:
> 
> > You ignored my question for explanation
> > why this is nonsense needed.
> 
> Sorry, but I fail to understand what 
> explanation I could add:
> 18 months ago, I posted three patches to 
> fix a user-reported issue, one was ok'ed, 
> another one was preferred, I committed the 
> preferred patch.
> It caused a regression, so Michael suggested 
> to get back to the other ok'ed patch which 
> I updated and applied.
> 
> Sorry, but I cannot add more explanation.

why are the codec_tag lists needed ?

every muxer should either have no codec_tag list or a list that is as
complete as possible.
matroska uses strings in some cases and int32 in others to identify
codecs. previously only the int32 based codecs where listed

IIRC:
This incomplete list caused confusion because when things where stream
copied the source had a tag X and an codec_id Y
and now matroskas codec_tag list contained no codec_id Y at all but
a entirely different codec with tag codec_tag X
this then led to the code stoping with an error
(the inconsistency that stoped things was stream copy specific though
 normal encoding would not stop as the mismatching tag doesnt occur
 there)

If OTOH theres a entry for codec_id Y with some tag then the type
can be stream copied into matroska. The 0xFFFFFFFF tag should not be
stored its just a random value for the table. One could replace these
by indexes into a string table of proper matroska codec tag strings.

[...]

-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Concerning the gods, I have no means of knowing whether they exist or not
or of what sort they may be, because of the obscurity of the subject, and
the brevity of human life -- Protagoras
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