function youtube_video(input)
{
  var link = window.prompt('Insert youtube video link.','http://www.youtube.com/watch?v=xxxxxxxxxxx');
  if(link)
  {
    var id_split1 = link.split('?v=');
    var id_split2 = id_split1[1].split('&');
    var id = id_split2[0];
    document.getElementById(input).value += '[youtube]'+id+'[/youtube]';
  }
}