[FFmpeg-trac] #8452(undetermined:closed): slow png decode starting with ffmpeg-3.3.1

[FFmpeg]

#8452: slow png decode starting with ffmpeg-3.3.1
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             Reporter:  DonMoir      |                    Owner:
                 Type:  defect       |                   Status:  closed
             Priority:  normal       |                Component:
                                     |  undetermined
              Version:  unspecified  |               Resolution:
                                     |  worksforme
             Keywords:  regression   |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
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Comment (by pdr0):

 I can replicate the issue with an 8bit PNG sequence. Windows x64

 I tested 3.2.4 vs. current. The old version is roughly 2x faster, similar
 to DonMoir's observations

 My observations:
 - RGB24 (suggests problem isn't alpha channel related)
 - image sequence (suggests it's not MOV or other container related)
 - 1000 frames (so test isn't too short)
 - multiple runs, repeatable (not some "outlier" or random event)
 - SSD (not I/O limited)
 - forcing -threads "x" doesn't help (where "x" is some number low or high)
 - relationship holds whether decoded as rawvideo (-c:v rawvideo), or just
 passed through as null (wrapped AV frame)

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Ticket URL: <https://trac.ffmpeg.org/ticket/8452#comment:7>
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