speed up or speed down whole or a part of a video #ffmpeg

ffspeed.sh

#!/bin/sh
_usage="Usage:\n    ffspeed input output speed\n    ffspeed input output speed from\n    ffspeed input output speed from to"
_version="0.0.1"

function display_usage() { 
	echo -e "\nffspeed version $_version"
	echo -e "$_usage" 
} 

function all_speed {
	FILE=$1
	OUTFILE=$2
	SPEED=$3
	FPS=$(ffmpeg -i $FILE 2>&1 | sed -n "s/.*, \(.*\) fp.*/\1/p")
	ffmpeg -i $FILE \
		-r $FPS*$SPEED -preset superfast -profile:v baseline \
		-filter_complex "[0:v]setpts=(1/$SPEED)*PTS[v];[0:a]atempo=$SPEED[a]" -map "[v]" -map "[a]" $OUTFILE
}

function part_speed () {
	FILE=$1
	OUTFILE=$2
	SPEED=$3
	START=$4
	END=$5
  
  # if END is not provided set end of the file
	if [ -z $5 ]
	then
		END=$(ffprobe -v error -show_entries format=duration -of default=noprint_wrappers=1:nokey=1 $FILE)
	fi
  
	ffmpeg -i $FILE \
	  -filter_complex \
	     "[0:v]trim=0:$START,setpts=PTS-STARTPTS[v1];
	      [0:v]trim=$START:$END,setpts=(1/$SPEED)*(PTS-STARTPTS)[v2];
	      [0:v]trim=$END,setpts=PTS-STARTPTS[v3];
	      [0:a]atrim=0:$START,asetpts=PTS-STARTPTS[a1];
	      [0:a]atrim=$START:$END,asetpts=PTS-STARTPTS,atempo=$SPEED[a2];
	      [0:a]atrim=$END,asetpts=PTS-STARTPTS[a3];
	      [v1][a1][v2][a2][v3][a3]concat=n=3:v=1:a=1" \
	  -preset superfast -profile:v baseline $OUTFILE
}

if [[ "$*" == "--help" || "$*" == "-h" || $# -eq 0 ]]
then
	display_usage
	exit 0
elif [  $# -le 3 ]
then
	echo -e "\nERROR: not enough arguments"
	display_usage
	exit 1
elif [  $# -eq 3 ]
then
	all_speed $1 $2 $3
	exit 0
elif [  $# -gt 3 ]
then
	part_speed $1 $2 $3 $4 $5
	exit 0
fi

wget -q https://gist.githubusercontent.com/7aman/d3b6931a8884614bcb843003d3138113/raw/97bd39df2ef237a550cb991aeaa027720031f705/ffspeed.sh
chmod u+x ffspeed.sh
# Usage
./ffspeed.sh input.mp4 output.mp4 3
# or
./ffspeed.sh input.mp4 output.mp4 3 120 240