Blend original video with edge detection filter output using multiply operator with ffmpeg, and accelerate slow motion video/audio

ffmpeg-composite-faster.sh

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

# the settings below converts from 480fps played at 30fps (1/8 speed slowmotion from Galaxy S9+)
# to 1/2 speed slow motion video at 60fps 
SPEED_FACTOR=4
OUTPUT_FRAMERATE=60

FACTOR=$(printf %.3f "$((10**3 * 1/$SPEED_FACTOR))e-3")

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 "$INPUT" \
  -filter_complex " \
    [0:v]setpts=$FACTOR*PTS[vid];
    [0:a]atempo=$SPEED_FACTOR;
    [0:v]setpts=$FACTOR*PTS,sobel=planes=0xf:scale=1,negate [sob]; \
    [vid][sob]blend=all_mode=multiply \
  " \
  -preset veryslow \
  -tune film \
  -r $OUTPUT_FRAMERATE \
  -crf 15 \
  -c:a aac \
  -b:a 128k \
  -pix_fmt yuv420p \
  -movflags \
  +faststart \
  "$OUTPUT"