use warnings;
use strict;
use DateTime::Duration;
use DateTime::Format::Duration;

my $first = "00:00:01:04";
my $last  = "00:00:08:861";

sub my_parse_duration {
	my $in = shift;
	my %t; @t{qw/hours minutes seconds nanoseconds/}
		= $in=~/\A(\d\d):(\d\d):(\d\d):(\d\d\d?)\z/
			or die "failed to parse '$in'";
	$t{nanoseconds}*=1000000; # ms->ns
	return DateTime::Duration->new(%t);
}
$first = my_parse_duration($first);
$last  = my_parse_duration($last );

my $fmt_out = DateTime::Format::Duration->new(
	pattern=>'%H:%M:%S:%3N', normalize=>1 );

print $fmt_out->format_duration($first),"\n";
print $fmt_out->format_duration($last ),"\n";
$last->subtract_duration($first);
print $fmt_out->format_duration($last ),"\n";

__END__

00:00:01:004
00:00:08:861
00:00:07:857