#!/usr/bin/perl

#####
#   
#   This script scales an input video to be the duration provided.
#
#   usage:
#       scale-video.pl [-a audiofile] [-b bitrate] -d hh:mm:ss infile outfile
#
#   The bitrate should be in kbps
#
#####

use strict;
use warnings;
use Getopt::Std;

my %opts;
getopts('a:b:d:', \%opts);
my ($src, $dst) = @ARGV;

## Convert a H:M:S duration into seconds ##
sub convert_duration {
    my @time_parts = reverse(split(":", $_[0]));
    my $accum = 0;
    for (my $i = 0; $i < @time_parts; $i++) {
        $accum += $time_parts[$i] * 60 ** $i;
    }
    return $accum;
}
###########################################

## Check for a custom bitrate ##
my $bitrate  = $opts{b} ? $opts{b} : 300;

## Parse the target duration ##
my $duration_dst = $opts{d} ?
    convert_duration($opts{d})
:(sub{
    print STDERR "No target duration found, use option -d\n";
    exit(1);
})->();

## Get input file's duration ##
my $probe = join(" ", grep /Duration/, `ffprobe $src 2>&1`);
my $duration_src = convert_duration(
    join(" ", $probe =~ /Duration:(?<duration>[^,]+)/));

## Mix in audio if we need to
my $audio = $opts{a} ? "-i \"$opts{a}\"" : "";

## If we have an input and output file attempt to convert
if (@ARGV == 2) {
    my $pts_value = $duration_dst / $duration_src;
    `ffmpeg $audio -i $src -b $bitrate"."k -vf "setpts=($pts_value)*PTS" $dst`;
} else {
    print STDERR "Requires a single source and destination file.\n";
    exit(1);
}