function OpenWindow(URL,Nome,propriedades) {
  window.open(URL,Nome,propriedades);
}
function play() {
window.parent.playerivals.document.location='play.htm';
window.parent.plai = "hidden";
window.parent.estope = "visible";
}
function stop() {
window.parent.playerivals.document.location='stop.htm';
window.parent.plai = "visible";
window.parent.estope = "hidden";
}

function mostra() {
         try {
         botao_play.style.visibility = window.parent.plai;
         botao_stop.style.visibility = window.parent.estope;
         } catch(err) {

         }
         
}
setInterval("mostra()",100);