converting png frames to gif is broken

[AyrA]

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

[AyrA]

Input PNG frames, example commands, generated GIF files

[Elon Musk]

The first issue is bug in swscale - it badly converts pal to other formats, workaround is using black color for transparency with palettegen.

[Carl Eugen Hoyos]

Is there any difference between this ticket and ticket #7902 (and #8584)?

[AyrA]

This one is about ffmpeg inserting lines of red (and sometimes green) color. The other ones aren't.

[Carl Eugen Hoyos]

Not gif-related afaict.

[Elon Musk]

The issue with green frame with new=1 have been fixed.

[Elon Musk]

Fixed in 79934cc702fe1c90bfb58bb83ab20490b9d86e37