[FFmpeg-devel] [PATCH 05/11] avcodec/h264_parser: Reuse the RBSP buffer

[Andreas Rheinhardt]

Kieran Kunhya:
> On Fri, 16 Aug 2019 at 04:20, Andreas Rheinhardt <
> andreas.rheinhardt at gmail.com> wrote:
> 
>> Up until now, the H.264 parser has allocated a new buffer for every
>> frame in order to store the unescaped RBSP in case the part of the RBSP
>> that will be unescaped contains 0x03 escape bytes. This is expensive
>> and this commit changes this: The buffer is now kept and reused.
>>
>> For an AVC file with an average framesize of 15304 B (without in-band
>> parameter sets etc.) and 132044 frames (131072 of which ended up in the
>> results) this reduced the average time used by the H.264 parser from
>> 87708 decicycles (excluding about 1100-1200 skips in each iteration)
>> to 16963 decicycles (excluding about 10-15 skips in each iteration).
>> The test has been iterated 10 times.
>>
> 
> If I understand correctly, this patch means if you have a large frame (or
> large NAL) you are stuck with the large allocation of memory until the
> decoder is closed.
> Not sure if you have read the discussion here
> https://patchwork.ffmpeg.org/patch/5631/
> 
> Kieran
> 
I am aware of said discussion; and also of your solution [1] to it. It
actually does exactly the same as I propose for the parser: It keeps a
single buffer that does not shrink. Given that this is used for the
decoders (and for cbs_h2645), I didn't deem this to be problematic.
(There is clearly no quadratic memory usage and what Derek warns about
(with huge NALs at specific positions) is a no issue for both.)

- Andreas

[1]: https://ffmpeg.org/pipermail/ffmpeg-devel/2017-November/219100.html