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

[Andreas Rheinhardt]

Andreas Rheinhardt:
> Andreas Rheinhardt:
>> On Fri, Feb 28, 2020 at 6:10 AM Andreas Rheinhardt <
>> andreas.rheinhardt at gmail.com> wrote:
>>
>>> On Tue, Feb 25, 2020 at 2:24 PM Andreas Rheinhardt <
>>> andreas.rheinhardt at gmail.com> wrote:
>>>
>>>> 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
>>>>
>>>
>>> Ping.
>>>
>>> - Andreas
>>>
>>
>> Ping.
>>
>> - Andreas
>>
> Ping.
> 
> - Andreas
> 
Ping.

- Andreas