Parse YouTube duration string to seconds integer

youTubeDurationParser.php

<?php
  /**
   * Match pattern PT#H#M#S (leading PT, hours, minutes, seconds) and return seconds value.
   *
   * @param string $string
   * @return int
   */
  private static function convertDuration($string)
  {   
      // Comprehensive regex that should match any value.
      // Keys:
      // 0 => Original string
      // 5 => Hours
      // 6 => Minutes
      // 7 => Seconds
      preg_match('/^(-|)?P([0-9]+Y|)?([0-9]+M|)?([0-9]+D|)?T?([0-9]+H|)?([0-9]+M|)?([0-9]+S|)?$/', $string, $matches);

      // Strip leading characters.
      foreach($matches as &$match):
          $match = intval(preg_replace('/((?!([0-9]|-)).)*/', '', $match));
      endforeach;

      // Return total seconds.
      return ($match[5] * 3600) + ($match[6] * 60) + $match[7];
  }