FFMPEG filter to boxblur and greyscale a video using alpha mask

Solution 1:

Here's a method using alphamerge, hue, boxblur, and overlay.

original blurred mask

_{Original input, filtered output, mask image.}

Example:

ffmpeg -i input -loop 1 -i mask.png -filter_complex \
"[0:v][1:v]alphamerge,hue=s=0,boxblur=5[fg]; \
 [0:v][fg]overlay[v]" -map "[v]" -map 0:a -c:a copy output

The mask should be the same size as the input. If it isn't you could use scale or scale2ref to resize it.
The audio is stream copied to avoid unnecessary encoding.

FFMPEG filter to boxblur and greyscale a video using alpha mask

Solution 1:

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