<html>
<head>
<script>
    function handlePlaying() {
        try {
            window.webkit.messageHandlers.testHandler.postMessage("playing");
        } catch(e) {
        }
    }
</script>
</head>
<body>
    <video autoplay src="large-video-with-audio.mp4" width=65536 height=65536 onplaying=handlePlaying()></video>
</body>
</html>