[FFmpeg-trac] #6768(ffmpeg:new): no png output allowed

[FFmpeg]

#6768: no png output allowed
-------------------------------------+-------------------------------------
             Reporter:  ftouvet      |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:  ffmpeg       |                  Version:
             Keywords:  png, image,  |  unspecified
  encoding                           |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug:
 I want to scale a png file into another png file, and ffmpeg crashes when
 writing the file. Even a simple copy is not ok.
 PNG-> JPEG is ok, JPEG -> PNG is ok, PNG -> PNG is not ok.
 I just updated from an old 2015 version, which was doing the operation
 without a warning.

 How to reproduce:
 {{{
 % ffmpeg -i my_source.png my_destination.png
 ffmpeg version N-87871-g7480f232d2 Copyright (c) 2000-2017 the FFmpeg
 developers

   built with gcc 7.2.0 (GCC)
   configuration: --enable-gpl --enable-version3 --enable-sdl2 --enable-
 bzlib --enable-fontconfig --enable-gnutls --enable-iconv --enable-libass
 --enable-libbluray --enable-libfreetype --enable-libmp3lame --enable-
 libopenjpeg --enable-libopus --enable-libshine --enable-libsnappy
 --enable-libsoxr --enable-libtheora --enable-libtwolame --enable-libvpx
 --enable-libwavpack --enable-libwebp --enable-libx264 --enable-libx265
 --enable-libxml2 --enable-libzimg --enable-lzma --enable-zlib --enable-gmp
 --enable-libvidstab --enable-libvorbis --enable-cuda --enable-cuvid
 --enable-d3d11va --enable-nvenc --enable-dxva2 --enable-avisynth --enable-
 libmfx
   libavutil      55. 79.100 / 55. 79.100
   libavcodec     57.108.100 / 57.108.100
   libavformat    57. 84.100 / 57. 84.100
   libavdevice    57. 11.100 / 57. 11.100
   libavfilter     6.108.100 /  6.108.100
   libswscale      4.  9.100 /  4.  9.100
   libswresample   2. 10.100 /  2. 10.100
   libpostproc    54.  8.100 / 54.  8.100
 }}}

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Ticket URL: <https://trac.ffmpeg.org/ticket/6768>
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