boxblurΒΆ

Watch on youtube.com
doc

https://ffmpeg.org/ffmpeg-filters.html#boxblur, https://en.wikipedia.org/wiki/Box_blur

  • xxx_radius: an expression for the box radius in pixels used for blurring the corresponding input plane.

  • xxx_power: how many times the boxblur filter is applied to the corresponding plane.

#! /bin/sh
ifn="Grape_Vineyard.mp4"
ifnb="`basename \"${ifn}\" .mp4`"
pref="`basename $0 .sh`"

# luma radius: 0 ... 250
# luma power
luma_radius=${luma_radius:-2}
luma_power=${luma_power:-4}
#
ffmpeg -y -i "${ifn}" -filter_complex "
[0:v]split[0v1][0v2];

[0v1]crop=900:500:30:580,setsar=1,
boxblur='lr=${luma_radius}:lp=${luma_power}'

,drawbox=c=blue[b];

[0v2][b]overlay=30:580[v]
" -map '[v]' -an "${pref}_${ifnb}.mp4"

You can specify an expression as value, but if what you need is someshat interesting visual effect, it will make you disappoint. Due to the lack of usable constants, we can only write to not depend on the size of the input video at best.