<!DOCTYPE html>
<html>
<head>
    <script>
        function loaded() {
            try {
                window.webkit.messageHandlers.testHandler.postMessage("loaded");
            } catch(e) { }
        }

        function play() {
            document.getElementById("video").play().then(function() {
                try {
                    window.webkit.messageHandlers.testHandler.postMessage("playing");
                } catch(e) { }
            });
        }
    </script>
</head>

<body onload="loaded()">
    <video id="video" controls src="test.mp4"></video>
</body>
</html>