FFmpeg split and set initial video incrementer

ffmpeg-splliter.sh

#!/bin/bash

read -e -r -p 'input file? ' in; 
read -e -i 'edited/' -r -p 'out dir? ' outDir; 
read -e -r -p 'out file prefix? ' out; 
read -e -i '1' -r -p 'start counter from which number? ' startCounter; 
read -e -i '00:05:00' -r -p 'split size? ' splitSize; 

tmpdir=$(mktemp -d)
outDir=$(echo $outDir | grep -o ".*[^/]")
mkdir -p "${outDir}"

echo "> splitting"
ffmpeg -i "${in}" -c copy -map 0 -segment_time "${splitSize}" \
-f segment -reset_timestamps 1 "${tmpdir}/${out}-%03d.mp4"

echo "> updating incrementer"
for f in $tmpdir/*.mp4; do 
  n=$(echo $f | grep -oP '\K([0-9]{3})(?=\.mp4)'); 
  if [ "$n" = "" ]; then
  	continue;
  fi
  fname=$(basename $f)
  newN=$(printf "%03d" $(expr $n + $startCounter)); 
  nf=$(echo ${fname} | sed "s/$n/$newN/");
  mv "$f" "${outDir}/$nf"
done;