/**
 * Convert ISO 8601 duration to mm:ss format
 */
function yt_format_duration($iso) {
    $interval = new DateInterval($iso);
    $totalSeconds = ($interval->h * 3600) + ($interval->i * 60) + $interval->s;
    return gmdate($totalSeconds >= 3600 ? "H:i:s" : "i:s", $totalSeconds);
}