You want the “Interactive Frames for Live Streams and VODs” bit, not that one.
It uses ‘Player’ not ‘Embed’
<html>
<body>
<script src= "http://player.twitch.tv/js/embed/v1.js"></script>
<div id="player"></div>
<script type="text/javascript">
var options = {
width: 1280,
height: 720,
channel: "monstercat",
autoplay: false,
};
var player = new Twitch.Player("player", options);
player.setVolume(0.5);
</script>
</body>
</html>