function rolly(img_name, img_src){
  document[img_name].innerHTML = ''+img_src+'';
}


function roll(img_name, img_src){
  document[img_name].src = img_src;
}

function getScreen( url, size )
{
  if(url === null){ return ""; }

  size = (size === null) ? "big" : size;
  var vid;
  var results;

  results = url.match("[\\?&]v=([^&#]*)");

  vid = ( results === null ) ? url : results[1];

  if(size == "small"){
    return "http://img.youtube.com/vi/"+vid+"/2.jpg";
  }else {
    return "http://img.youtube.com/vi/"+vid+"/0.jpg";
  }
}