[FFmpeg-devel] [PATCH v3] avformat/matroskaenc: Use random TrackUID

Andreas Rheinhardt andreas.rheinhardt at gmail.com
Fri Dec 6 01:59:00 EET 2019

Michael Niedermayer:
> On Tue, Dec 03, 2019 at 04:19:47PM +0100, Andreas Rheinhardt wrote:
>> Up until now, the TrackUID of a Matroska track which is supposed to be
>> random was not random at all: It always coincided with the TrackNumber
>> which is usually the 1-based index of the corresponding stream in the
>> array of AVStreams. This has been changed: It is now set via an AVLFG
>> if AVFMT_FLAG_BITEXACT is not set. Otherwise it is set like it is set
>> now (the only change happens if an explicit track number has been
>> chosen via dash_track_number, because the system used in the normal
>> situation is now used, too). In particular, no FATE tests need to be
>> updated.
>> This also fixes a bug in case the dash_track_number option was used:
>> In this case the TrackUID was set to the track number, but the tags were
>> written with a TagTrackUID simply based upon the index, so that the tags
>> didn't apply to the track they ought to apply to.
> thx
Good to hear. When merging, the fix for ChapterUIDs
should get merged first.
>> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
>> ---
>> I have updated the patchset to rely on the AVLFG to provide sufficiently
>> many distinct values, as you said. I could add a check and a for if we still
>> have a collision after (say) 1000 tries in order to avoid the
>> potentially infinite loop.
> You could replace the LFG if you dont trust it.
> But i dont understand why you would use it when you dont trust it and then
> add a check
I actually trust that it works; it's just that I can't furnish a proof.

- Andreas

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