http://learn.javascript.ru/play/LWz8f
<!DOCTYPE HTML>
<html>
<head> </head>
<body>
<iframe id="player" height="249" scrolling="no" width="320"></iframe>
<br>
<button onclick="changePlayer('https://www.youtube.com/embed/vUmLfvHkGus')">Player 1</button>
<button onclick="changePlayer('https://vk.com/video_ext.php?oid=11767786&id=169403336&hash=a1a5d2c281b53598&hd=2')">Player 2</button>
<script type="text/javascript">
var player = document.getElementById('player');
function changePlayer(src) {
player.src = src;
};
changePlayer('https://www.youtube.com/embed/vUmLfvHkGus');
</script>
</body>
</html>