[FFmpeg-trac] #8453(undetermined:new): converting png frames to gif is broken

[FFmpeg]

#8453: converting png frames to gif is broken
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             Reporter:  AyrA         |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:  git-
  undetermined                       |  master
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
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 == Summary of the bug ==

 Converting png frames with transparency creates weird looking animations.
 - The first non-transparent row of each frame is replaced with a semi-
 transparent red line, sometimes other colors.
 - Using local palette occasionally replaces the transparent sections with
 green
 - The frame disposal is set to "replace" instead of "combine"

 == Version Info ==

 OS: Windows 7 SP1 x64

 ffmpeg: git-2019-12-29-e20c6d9

 Note: The issue with the frame disposal and transparency being green does
 not exists in version N-91266-g8c20ea8ee0. The issue with the horizontal
 lines exists in both versions

 == How to reproduce ==

 Using a global palette:

 {{{
 ffmpeg -framerate 2 -i %02d.png -filter_complex "[0:v] split [a][b];[a]
 palettegen [p];[b][p] paletteuse" test.gif
 }}}

 Using a local palette (one for each frame):

 {{{
 ffmpeg -framerate 2 -i %02d.png -filter_complex "[0:v] split [a][b];[a]
 palettegen=stats_mode=single [p];[b][p] paletteuse=new=1" test.gif
 }}}

 Note: attached are the frames as well as generated outputs

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Ticket URL: <https://trac.ffmpeg.org/ticket/8453>
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