<!DOCTYPE html>
<html>
<script>
    function beganAutoplaying() {
        setTimeout(function() {
            try {
                window.webkit.messageHandlers.testHandler.postMessage("autoplayed");
            } catch(e) {
            }
        }, 0)
    }
</script>
<body>
    <video id="foo" style="width: 480px; height: 320px;"><source src="large-video-with-audio.mp4"></video>
    <video autoplay onplaying=beganAutoplaying() id="bar" style="width: 480px; height: 320px;"><source src="large-video-with-audio.mp4"></video>
    <video id="baz" style="width: 480px; height: 320px;"><source src="large-video-with-audio.mp4"></video>
</body>
<html>