Fix Subtitle Offset

#!/bin/bash
# Filename: srt-fix-offset.sh
# Version.: 20052018
# Author..: not robz
# A script to modify subtitle offset beyond the Kodi maximum of 60 seconds.
# Put original titles in a file called "srt.txt" in your home directory and
# run the script.
# In all honesty this is pretty much a copy paste job from Linux Questions.
# For more detailed information goto:
# www.linuxquestions.org/questions/linux-newbie-8/editing-srt-files-4175436550/
#
# Modify and comment the offset variable as appropriate.
# Advance subtitles.
offset="75 seconds"
# Retard subtiles.
#offset="5 seconds ago"

while read start s end; do
    if [[ $start =~ ^..:..:..,... ]]; then
        start=$(date -d "$start $offset" +%H:%M:%S,%N)
        end=$(date -d "$end $offset" +%H:%M:%S,%N)
        echo ${start:0:12} $s ${end:0:12}
    else
        echo $start $s $end
    fi
done < srt.txt >> new-subtitles.srt