How can I add a progress bar to WWW::Mecha​nize

$m->get($u, ":content_cb" => \&callback);

open (VID,">$i.flv") or die "$!";
$total = 0;
sub callback
{
    my( $data, $response, $proto ) = @_;
    print VID "$data"; # write data to file
    $total+= length($data);
    $size = $response->header('Content-Length');
    print floor(($total/$size)*100),"% downloaded\n"; # print percent downloaded
}