function add_video_wmode_transparent($html, $url, $attr) {
   if (strpos($html, "<embed" ) !== false) {
    	$html = str_replace('</param><embed', '</param><param name="wmode" value="transparent"></param><embed wmode="transparent" ', $html);
   		return $html;
   } else {
        return $html;
   }
}
add_filter('embed_oembed_html', 'add_video_wmode_transparent', 10, 3);