For anyone remotely interested, I managed to fix the problem by doing the following :-
<?php
$path = '/mnt/data/video/films/';
$filename = htmlspecialchars($_GET["file"]);
$ext=strrchr($filename, ".");
$file = $path . $filename;
ob_start();
passthru("/usr/local/bin/ffmpeg -i \"". $file . "\" 2>&1");
$duration = ob_get_contents();
ob_end_clean();
preg_match('/Duration: (.*?),/', $duration, $matches);
$duration = $matches[1];
list($hr,$m,$s) = explode(':', $duration);
$duration_in_seconds = ( (int)$hr*3600 ) + ( (int)$m*60 ) + (int)$s;
// a work around for now - need to remove when above works
//$duration_in_seconds = 10800
//}
?>
It only took one whole day to figure out (as my php coding skills are weak).
RD