function bb_parse($string) 
{
  $tags = 'b|i|size|color|center|quote|url|img|video';
  while (preg_match_all('`\[('.$tags.')=?(.*?)\](.+?)\[/\1\]`', $string, $matches)) foreach ($matches[0] as $key => $match) {
    list($tag, $param, $innertext) = array($matches[1][$key], $matches[2][$key], $matches[3][$key]);
    switch ($tag) {
        case 'b': $replacement = "$innertext"; break;
        case 'i': $replacement = "$innertext"; break;
        case 'size': $replacement = "$innertext"; break;
        case 'color': $replacement = "$innertext"; break;
        case 'center': $replacement = "
$innertext
"; break;
        case 'quote': $replacement = "
$innertext
" . $param? "$param" : ''; break;
        case 'url': $replacement = '$innertext"; break;
        case 'img':
          list($width, $height) = preg_split('`[Xx]`', $param);
          $replacement = "';
        break;
        case 'video':
          $videourl = parse_url($innertext);
          parse_str($videourl['query'], $videoquery);
          if (strpos($videourl['host'], 'youtube.com') !== FALSE) $replacement = '';
          if (strpos($videourl['host'], 'google.com') !== FALSE) $replacement = '';
        break;
    }
    $string = str_replace($match, $replacement, $string);
  }
  return $string;
}