subshift /data/subtitle.srt - 3:42 > /data/newsubtitle.srt

##</code><code>##

subshift /data/subtitle.srt + 1:5:32,242 > /data/newsubtitle.srt

##</code><code>##

#!/usr/bin/perl

use strict;
use warnings;

#############################################
# init

my ( $infile, $oper, $shiftime ) = @ARGV;

usage() if not ( $infile and $oper and $shiftime);
usage() if ( $oper ne "+" and $oper ne "-" );

#############################################
# main

open my $fh, "<", $infile or die "error opening '$infile':$!";

$shiftime = time_to_sec($shiftime);

while (<$fh>) {
	if ( m/^(\d{2}:\d{2}:\d{2},\d+)\s\-\-\>\s(\d{2}:\d{2}:\d{2},\d+)/ ) {
		my ($start, $end) = ( $1, $2);
		
		my $startsec = time_to_sec($start);
		my $endsec = time_to_sec($end);
		
		if ( $oper eq "+" ) {
			$startsec += $shiftime;
			$endsec += $shiftime;
		} else {
			# bug : should check that time stays positive
			$startsec -= $shiftime;
			$endsec -= $shiftime;
		}
		
		$start = sec_to_time($startsec);
		$end= sec_to_time($endsec);
		
		print "$start --> $end\r\n";
	} else {
		print $_ ;
	}
}


close $fh;


#############################################
# subs

sub usage {
	print "usage : $0 <file> <+|-> <duration>\n\n";
	print "duration is expressed in hours:minutes:secondes,milliseconds.\nLeading zeros are optional.\n";
	print "result output to stdout.\n";
	exit 1;
}

sub time_to_sec {
	my $time = shift;
	
	my @elems = split(':', $time);
	my $seconds = pop @elems;
	my $minutes = pop @elems;
	my $hours   = pop @elems;
	
	$seconds =~ s/,/./g;
	
	# force to numerical
	$hours += 0; $minutes += 0; $seconds += 0;
	
	# convert to seconds for easier manipulation
	my $time_sec =  ( $hours * 3600 ) + ($minutes * 60 ) + $seconds ;

	return $time_sec;
}

sub sec_to_time {
	my $sectime = shift;
	
	my $hours = sprintf( "%02d", int ( $sectime / 3600 ) );
	my $minutes =  sprintf( "%02d", int ( ( $sectime - ( $hours * 3600 ) ) / 60 ) );
	my $seconds = sprintf( "%02.3f", ( ( $sectime - ( $hours * 3600 ) ) - ( $minutes * 60 )) );
	
	$seconds =~ s/\./,/g;
	
	return "$hours:$minutes:$seconds";
}