#!/usr/bin/perl
use strict;
use warnings;

use POSIX qw/strftime/;
use CGI qw/:standard/;

sub handle_error($)
{
my $msg = shift or die;
print header(-type => 'text/plain'), $msg;
die;
}

my $num_frames = 7;
my $thumb_dir = '/tmp';
my $thumb_offset_pct = 15;
my $thumb_offset;
my $thumb_pathname;
my $video_pathname = param('dir') or die;
$video_pathname .= '/' . param('filename') or die;

# clean up from previous incarnations
# TODO make this multi-user capable, so that muliple simultaneous instances do not walk on each other
for (1..$num_frames+1)
        {
        $thumb_pathname = sprintf("%s/%8.8d.jpg", $thumb_dir, $_);
        unlink $thumb_pathname or die if -f $thumb_pathname;
        }

# determine the length of the video
my ($video_len) = grep(/^ID_LENGTH=/, (`mplayer -identify \"$video_pathname\" -nosound -vc dummy -vo null`));
if ( $video_len !~ /^[^=]+=(.*)$/ )
        {
        die 'Unable to read video length';
        }
$video_len = $1;

# this mplayer command will produce a series of JPEG images, one of which will be our thumbnail
$thumb_offset = int( $video_len * $thumb_offset_pct / 100 );
my $cmd = "mplayer -zoom -ss $thumb_offset -nosound -vo jpeg:outdir=/tmp -frames $num_frames -vf scale=250:-3 \"$video_pathname\" > /dev/null 2>&1";
my $retval = system($cmd);
#handle_error 'Command failed: ' . $cmd if $retval != 0;

binmode STDOUT;

# choose the highest numbered frame, since lower numbered
# frames tend to be incomplete.
my $frame = $num_frames + 1;
while ($frame ge 1)
        {
        $thumb_pathname = sprintf("%s/%8.8d.jpg", $thumb_dir, $frame);
        last if -f $thumb_pathname;
        $frame--;
        }
handle_error 'No thumbnail created.' if ! -f $thumb_pathname;

# now we have chosen the right pathname

# get the last-modified timestamp for the video in question,
# so that we can set the HTTP last-modified header.
my @info        = stat($video_pathname) or die 'Unable to stat() video';
my @ts          = gmtime($info[9]);
my $timestamp   = strftime("%a, %d %b %Y %H:%M:%S GMT", @ts);

open IMG, '<' . $thumb_pathname or die 'Unable to open thumbnail';

print   header( -type => 'image/jpeg', -last_modified => $timestamp);
print <IMG>;
close IMG;