The blend video filter allows to 'subtract' two frames from each other. But
I am unable to get this to work as I would expect with Gimp's color-erase.
This gives me an all transparent png (including the reversed input), it is
not what I expect, but at least it has a transparent output.
ffmpeg -i input.png -i input-green.png -filter_complex
"blend=all_mode=subtract" -vcodec png /tmp/test-blend.png
My input video gives me either a black background with green outlines, or a
black background with a fuchsia where white was.
ffmpeg -i test.mkv -i green.png -filter_complex "blend=all_mode=subtract"
-vcodec png /tmp/test-blend.mkv
The root cause seems to be that my input MPNG file is rgb24, and should be
rgba. The line below gives me a fully transparent image.
ffmpeg -y -i test.mkv -i green.png -filter_complex
"[0:v]format=rgba[v];[v][1:v]blend=all_mode=subtract[outv]" -map "[outv]"
-vcodec png /tmp/test-blend.mkv
What I am looking for is the output similar to color-erase.png. Is this
already possible with ffmpeg?
--
Stefan
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