#8533: complex_filter very slow when stichting together many fragments
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Reporter: stefanreich | Type: defect
Status: new | Priority: normal
Component: | Version:
undetermined | unspecified
Keywords: | Blocked By:
Blocking: | Reproduced by developer: 0
Analyzed by developer: 0 |
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Summary of the bug:
complex_filter turns very slow when splicing a long video into parts and
re-assembling them using complex_filter.
The script contains 894 parts which are taken from one input video and
assembled into a new one. When I run the command as shown, it starts with
less .01x realtime speed and very slowly goes up to around .1x. It keeps
climbing, but only very slowly. I noticed ffmpeg also doesn't use all the
cores anymore (only around 1.5 cores).
When I take less of those 894 parts, e.g. only 300, ffmpeg is noticeably
faster. With less than 100 parts, it runs in more than realtime as I
expect it to.
How is this explained? I can see no logical reason for this behavior,
processing speed should stay high even with many fragments (they are not
getting shorter, there are just fewer of them).
It really hinders my video editing of large videos using ffmpeg, so I
think this is an actual bug.
How to reproduce:
{{{
% ffmpeg -y -i winograd2-amp.mkv -filter_complex_script script.txt -map
[outv] -map [outa] winograd2-amp-cut.mkv
with this file: https://botcompany.de/files/1400345/complex-script.txt
ffmpeg version 3.4.6-0ubuntu0.18.04.1
built with gcc 7 (Ubuntu 7.3.0-16ubuntu3)
}}}
I can provide the input .mkv on request.
--
Ticket URL: <https://trac.ffmpeg.org/ticket/8533>
FFmpeg <https://ffmpeg.org>
FFmpeg issue tracker
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