I executed this code from my localhost and it worked
<!DOCTYPE html>
<html>
<head>
<script type="text/javascript" src="http://player.longtailvideo.com/jwplayer.js"></script>
</head>
<body>
<div id="container">Loading the player ...</div>
<script type="text/javascript">
jwplayer("container").setup({
flashplayer: "fwplayer.swf",
file: "https://www.youtube.com/watch?v=yourVideo",
skin: "mySkin.xml",
height: 270,
width: 480
});
</script>
</body>
</html>