usage:
$ awk -f srt.awk -v shift=<+-shift in seconds> infile.srt > outfile.srt
$ awk -f srt.awk -v shift=45.675 infile.srt > outfile.srt
positive values for shift make subs appear later, negative values make them appear sooner
srt.awk - lightweight awk script to shift timestamps in .srt sub files Copyright (C) 2021 ohnekopf
This program is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation; either version 2 of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for more details.