So your uncle recorded for you this old swedish movie on his DVR, and gave you a copy of it. You transcode it to XVID then realize that, Dammit! you haven't got the subtitles and your swedish really is cranky, so you get the subtitles from some website but alas, they're for some DVD version and begins more quickly (because there aren't the ads), or else.

So you need to edit those thousands of time entries in the .srt file to correct them. There comes my script to the rescue...

Let's say you need to shift the subtitles 3 minutes 42 seconds sooner... Simply do :

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

Now you may want to make it later by 1 hour, 5 minutes, 32 seconds and bananas :

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

#!/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,millisecond
+s.\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";
}
[download]

Edit: applied some corrections as suggested by jwkrahn.