Update content on the fly

Well if you are trying to replace width=”” where “” means empty, you do not need to use “*” when using str_replace, as str_replace do not support regular expression. In that case you function will be as :

function replace_content_on_the_fly($text){
    $replace = array(
        // 'words to find' => 'replace with this'
        'width=""' => 'width="730px"',
        'height=""' => 'height="486px"'

    );
    $text = str_replace(array_keys($replace), $replace, $text);
    return $text;
} 

If you want to replace all width height what so ever is between “”, you need to use preg_replace

function replace_content_on_the_fly($text){
      $newWidth = 730;
          $newHeight = 486;        

$text = preg_replace(
   array('/width="\d+"/i', '/height="\d+"/i'),
   array(sprintf('width="%d"', $newWidth), sprintf('height="%d"', $newHeight)),
   $text);

        return $text;
    }