[FFmpeg-devel] [PATCH 7/30] avformat/matroskaenc: Avoid allocations for SeekHead

Andreas Rheinhardt andreas.rheinhardt at gmail.com
Tue Feb 25 15:24:00 EET 2020

Andreas Rheinhardt:
> Andreas Rheinhardt:
>> Andreas Rheinhardt:
>>> Up until e7ddafd5, the Matroska muxer wrote two SeekHeads: One at the
>>> beginning referencing the main level 1 elements (i.e. not the Clusters)
>>> and one at the end, referencing the Clusters. This second SeekHead was
>>> useless and has therefore been removed. Yet the SeekHead-related
>>> functions and structures are still geared towards this usecase: They
>>> are built around an allocated array of variable size that gets
>>> reallocated every time an element is added to it although the maximum
>>> number of Seek entries is a small compile-time constant, so that one should
>>> rather include the array in the SeekHead structure itself; and said
>>> structure should be contained in the MatroskaMuxContext instead of being
>>> allocated separately.
>>> The earlier code reserved space for a SeekHead with 10 entries, although
>>> we currently write at most 6. Reducing said number implied that every
>>> Matroska/Webm file will be 84 bytes smaller and required to adapt
>>> several FATE tests; furthermore, the reserved amount overestimated the
>>> amount needed for for the SeekHead's length field and how many bytes
>>> need to be reserved to write a EBML Void element, bringing the total
>>> reduction to 89 bytes.
>>> Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt at gmail.com>
>>> ---
>> Ping.
>> - Andreas
> Ping (the actual patch (which has been omitted for brevity) is here:
> https://ffmpeg.org/pipermail/ffmpeg-devel/2020-February/256997.html).
> - Andreas
Another ping.

- Andreas

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