[FFmpeg-trac] #4443(undetermined:new): Transparency gets lost when using palettegen / paletteuse

[FFmpeg]

#4443: Transparency gets lost when using palettegen / paletteuse
-------------------------------------+-------------------------------------
               Reporter:  cehoyos    |                  Owner:
                   Type:  defect     |                 Status:  new
               Priority:  normal     |              Component:
                Version:  git-       |  undetermined
  master                             |               Keywords:  alpha
             Blocked By:             |               Blocking:
Reproduced by developer:  0          |  Analyzed by developer:  0
-------------------------------------+-------------------------------------
 When using palettegen / paletteuse to encode to pal8, transparency gets
 lost.
 {{{
 $ ffmpeg -i alpha.png -vf palettegen pal.png
 ffmpeg version N-71320-gc4b2017 Copyright (c) 2000-2015 the FFmpeg
 developers
   built with gcc 4.7 (SUSE Linux)
   configuration: --enable-gpl
   libavutil      54. 22.100 / 54. 22.100
   libavcodec     56. 34.100 / 56. 34.100
   libavformat    56. 29.100 / 56. 29.100
   libavdevice    56.  4.100 / 56.  4.100
   libavfilter     5. 13.101 /  5. 13.101
   libswscale      3.  1.101 /  3.  1.101
   libswresample   1.  1.100 /  1.  1.100
   libpostproc    53.  3.100 / 53.  3.100
 Input #0, png_pipe, from 'alpha.png':
   Duration: N/A, bitrate: N/A
     Stream #0:0: Video: png, pal8, 21x21 [SAR 5:6 DAR 5:6], 25 tbr, 25
 tbn, 25 tbc
 Output #0, apng, to 'pal.png':
   Metadata:
     encoder         : Lavf56.29.100
     Stream #0:0: Video: apng, rgba, 16x16 [SAR 1:1 DAR 1:1], q=2-31, 200
 kb/s, 25 fps, 25 tbn, 25 tbc
     Metadata:
       encoder         : Lavc56.34.100 apng
 Stream mapping:
   Stream #0:0 -> #0:0 (png (native) -> apng (native))
 Press [q] to stop, [?] for help
 [Parsed_palettegen_0 @ 0x35ec900] 4(+1) colors generated out of 4 colors;
 ratio=1.000000
 [apng @ 0x35f9040] Only a single frame so saving as a normal PNG.
 frame=    1 fps=0.0 q=0.0 Lsize=       0kB time=00:00:00.04 bitrate=
 24.2kbits/s
 video:0kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB
 muxing overhead: 30.107527%
 }}}
 {{{
 $ ffmpeg -i alpha.png -i pal.png -lavfi paletteuse out.gif
 ffmpeg version N-71320-gc4b2017 Copyright (c) 2000-2015 the FFmpeg
 developers
   built with gcc 4.7 (SUSE Linux)
   configuration: --enable-gpl
   libavutil      54. 22.100 / 54. 22.100
   libavcodec     56. 34.100 / 56. 34.100
   libavformat    56. 29.100 / 56. 29.100
   libavdevice    56.  4.100 / 56.  4.100
   libavfilter     5. 13.101 /  5. 13.101
   libswscale      3.  1.101 /  3.  1.101
   libswresample   1.  1.100 /  1.  1.100
   libpostproc    53.  3.100 / 53.  3.100
 Input #0, png_pipe, from 'alpha.png':
   Duration: N/A, bitrate: N/A
     Stream #0:0: Video: png, pal8, 21x21 [SAR 5:6 DAR 5:6], 25 tbr, 25
 tbn, 25 tbc
 Input #1, png_pipe, from 'pal.png':
   Duration: N/A, bitrate: N/A
     Stream #1:0: Video: png, rgba, 16x16, 25 tbr, 25 tbn, 25 tbc
 Output #0, gif, to 'out.gif':
   Metadata:
     encoder         : Lavf56.29.100
     Stream #0:0: Video: gif, pal8, 21x21 [SAR 5:6 DAR 5:6], q=2-31, 200
 kb/s, 25 fps, 100 tbn, 25 tbc (default)
     Metadata:
       encoder         : Lavc56.34.100 gif
 Stream mapping:
   Stream #0:0 (png) -> paletteuse:default
   Stream #1:0 (png) -> paletteuse:palette
   paletteuse -> Stream #0:0 (gif)
 Press [q] to stop, [?] for help
 frame=    1 fps=0.0 q=0.0 Lsize=       1kB time=00:00:00.04 bitrate=
 185.0kbits/s
 video:1kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB
 muxing overhead: unknown
 }}}

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Ticket URL: <https://trac.ffmpeg.org/ticket/4443>
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