mjpeg movies have lifted black

[fnordware]

Summary of the bug: If I start with a PNG sequence or ProRes? movie that has areas of black pixels and transcode to mjpeg, the black areas are not quite black. This can be verified by converting the mjpeg movie back to PNG.

How to reproduce:

% ffmpeg -i  -start_number 0 -framerate 30.0 -i input.%03d.png -c:v mjpeg -q 3 output.mov

% ffmpeg -i output.mov verify.%03d.png


ffmpeg version 4.0.2-tessus Copyright (c) 2000-2018 the FFmpeg developers
  built with Apple LLVM version 9.1.0 (clang-902.0.39.2)

[cehoyos]

You cannot convert png->jpg->png and expect identical output.

If this is a regression please also test current FFmpeg git head, test with the color filter and provide your command line together with the complete, uncut console output to make this a valid ticket.

[fnordware]

I realize there will be some loss going from PNG to mjpeg, but I still expect large black areas to stay black.

BUT...it seems to be fixed in the latest build, N-91991-gc02ff77681-tessus. Sorry about the needless trouble.