CSS

video {
  -webkit-transform-style: preserve-3d;
}

使用Javascript

$(document).ready(function(){
  $("#nav li").hover(
    function() {
      $(this).find('ul:first').css({visibility: "visible",display: "none"}).fadeIn(300);
      $("video").css({visibility:"hidden"});
    },function(){ 
      $(this).find('ul:first').css({visibility: "hidden"});
      $("video").css({visibility:"visible"});
    }
  );
);