Blend original video with edge detection filter output using multiply operator with ffmpeg

ffmpeg-composite.sh

#!/bin/bash
INPUT=$1
OUTPUT=$2

if [ -z "$OUTPUT" ] ; then
  EXT=${INPUT##*.}
  BASENAME=$(basename -- $INPUT .$EXT)
  OUTPUT=$(dirname $INPUT)/$BASENAME-composite.$EXT
fi

# to add some processing steps using filter_complex below (eg color correction)
# check https://ffmpeg.org/ffmpeg-filters.html

ffmpeg \
  -i "$INPUT" \
  -filter_complex " \
    [0:v]sobel=planes=0xf:scale=1,negate [sob]; \
    [0:v][sob]blend=all_mode=multiply \
  " \
  -preset veryslow \
  -tune film \
  -crf 15 \
  -c:a copy \
  -pix_fmt yuv420p \
  -movflags \
  +faststart \
  "$OUTPUT"