[FFmpeg-trac] #9334(undetermined:new): MP4 to APNG conversion incorrectly has transparent background

[FFmpeg]

#9334: MP4 to APNG conversion incorrectly has transparent background
-------------------------------------+-------------------------------------
             Reporter:  mcpower      |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:
  undetermined                       |  unspecified
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug: The attached black and white MP4 video (which has no
 alpha channel), when transcoded to APNG using ffmpeg results in the
 background being transparent.

 How to reproduce:
 {{{
 PS> ffmpeg -i black_and_white_splash.mp4 -plays 0
 black_and_white_splash.apng
 ffmpeg version 2021-07-14-git-ca56299fb3-full_build-www.gyan.dev Copyright
 (c) 2000-2021 the FFmpeg developers
   built with gcc 10.3.0 (Rev2, Built by MSYS2 project)
   configuration: --enable-gpl --enable-version3 --enable-static --disable-
 w32threads --disable-autodetect --enable-fontconfig --enable-iconv
 --enable-gnutls --enable-libxml2 --enable-gmp --enable-lzma --enable-
 libsnappy --enable-zlib --enable-librist --enable-libsrt --enable-libssh
 --enable-libzmq --enable-avisynth --enable-libbluray --enable-libcaca
 --enable-sdl2 --enable-libdav1d --enable-libzvbi --enable-librav1e
 --enable-libsvtav1 --enable-libwebp --enable-libx264 --enable-libx265
 --enable-libxvid --enable-libaom --enable-libopenjpeg --enable-libvpx
 --enable-libass --enable-frei0r --enable-libfreetype --enable-libfribidi
 --enable-libvidstab --enable-libvmaf --enable-libzimg --enable-amf
 --enable-cuda-llvm --enable-cuvid --enable-ffnvcodec --enable-nvdec
 --enable-nvenc --enable-d3d11va --enable-dxva2 --enable-libmfx --enable-
 libglslang --enable-vulkan --enable-opencl --enable-libcdio --enable-
 libgme --enable-libmodplug --enable-libopenmpt --enable-libopencore-amrwb
 --enable-libmp3lame --enable-libshine --enable-libtheora --enable-
 libtwolame --enable-libvo-amrwbenc --enable-libilbc --enable-libgsm
 --enable-libopencore-amrnb --enable-libopus --enable-libspeex --enable-
 libvorbis --enable-ladspa --enable-libbs2b --enable-libflite --enable-
 libmysofa --enable-librubberband --enable-libsoxr --enable-chromaprint
   libavutil      57.  0.100 / 57.  0.100
   libavcodec     59.  3.101 / 59.  3.101
   libavformat    59.  4.100 / 59.  4.100
   libavdevice    59.  0.100 / 59.  0.100
   libavfilter     8.  0.103 /  8.  0.103
   libswscale      6.  0.100 /  6.  0.100
   libswresample   4.  0.100 /  4.  0.100
   libpostproc    56.  0.100 / 56.  0.100
 Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'black_and_white_splash.mp4':
   Metadata:
     major_brand     : isom
     minor_version   : 512
     compatible_brands: isomiso2avc1mp41
     encoder         : Lavf59.4.100
   Duration: 00:00:02.37, start: 0.000000, bitrate: 63 kb/s
   Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv,
 bt709), 160x160 [SAR 1:1 DAR 1:1], 57 kb/s, 30 fps, 30 tbr, 15360 tbn
 (default)
     Metadata:
       handler_name    : VideoHandler
       vendor_id       : [0][0][0][0]
 Stream mapping:
   Stream #0:0 -> #0:0 (h264 (native) -> apng (native))
 Press [q] to stop, [?] for help
 Output #0, apng, to 'black_and_white_splash.apng':
   Metadata:
     major_brand     : isom
     minor_version   : 512
     compatible_brands: isomiso2avc1mp41
     encoder         : Lavf59.4.100
   Stream #0:0(und): Video: apng, rgb24(pc, bt709, progressive), 160x160
 [SAR 1:1 DAR 1:1], q=2-31, 200 kb/s, 30 fps, 30 tbn (default)
     Metadata:
       handler_name    : VideoHandler
       vendor_id       : [0][0][0][0]
       encoder         : Lavc59.3.101 apng
 frame=   71 fps=0.0 q=-0.0 Lsize=     182kB time=00:00:02.36 bitrate=
 629.6kbits/s speed=22.7x
 }}}

 Also reproduced with ffmpeg version 4.2.4-1ubuntu0.1.

 Attached is the input file, the output file, and a recording of the output
 APNG file as displayed in Google Chrome. Google Chrome uses an #e6e6e6
 (light grey) background behind all transparent backgrounds.
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/9334>
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