blend=grainextract doesn't work

[Michael Koch]

blend=grainextract should calculate the difference between two frames and shift the result to middle gray. If both frames are identical, the result should be uniform middle gray. But it isn't.

ffmpeg -f lavfi -i testsrc2 -lavfi split,blend=grainextract -frames 1 -y out.png

ffmpeg version 2022-04-18-git-d5687236ab-full_build-www.gyan.dev Copyright (c) 2000-2022 the FFmpeg developers

built with gcc 11.2.0 (Rev10, 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-bzlib --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-libdavs2 --enable-libuavs3d --enable-libzvbi --enable-librav1e --enable-libsvtav1 --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxavs2 --enable-libxvid --enable-libaom --enable-libopenjpeg --enable-libvpx --enable-mediafoundation --enable-libass --enable-frei0r --enable-libfreetype --enable-libfribidi --enable-liblensfun --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-libshaderc --enable-vulkan --enable-libplacebo --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. 24.101 / 57. 24.101
libavcodec 59. 26.100 / 59. 26.100
libavformat 59. 22.100 / 59. 22.100
libavdevice 59. 6.100 / 59. 6.100
libavfilter 8. 33.100 / 8. 33.100
libswscale 6. 6.100 / 6. 6.100
libswresample 4. 6.100 / 4. 6.100
libpostproc 56. 5.100 / 56. 5.100

Input #0, lavfi, from 'testsrc2':

Duration: N/A, start: 0.000000, bitrate: N/A
Stream #0:0: Video: rawvideo (I420 / 0x30323449), yuv420p, 320x240 [SAR 1:1 DAR 4:3], 25 tbr, 25 tbn

Stream mapping:

Stream #0:0 (rawvideo) -> split:default
blend:default -> Stream #0:0 (png)

Press [q] to stop, ? for help
Output #0, image2, to 'out.png':

Metadata:

encoder : Lavf59.22.100

Stream #0:0: Video: png, rgb24(pc, gbr/unknown/unknown, progressive), 320x240 [SAR 1:1 DAR 4:3], q=2-31, 200 kb/s, 25 fps, 25 tbn

Metadata:

encoder : Lavc59.26.100 png

frame= 1 fps=0.0 q=-0.0 Lsize=N/A time=00:00:00.04 bitrate=N/A speed=4.33x
video:4kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown

[Michael Koch]

sorry, I forgot "all_mode="
It works.