<!DOCTYPE html>
<html>
<style>
    video {
        width: 480px;
        height: 320px;
    }
    #bar {
        margin-top: 5000px;
    }
</style>
<script>
    function muteFirstVideoAndScrollToSecondVideo() {
        document.querySelector("#foo").muted = true;
        document.querySelector("#bar").scrollIntoView();
        setTimeout(function() {
            try {
                window.webkit.messageHandlers.testHandler.postMessage("playing");
            } catch(e) { }
        }, 0);
    }
    function beganAutoplaying() {
        setTimeout(function() {
            try {
                window.webkit.messageHandlers.testHandler.postMessage("autoplayed");
            } catch(e) {
            }
        }, 0)
    }
</script>
<body>
    <video autoplay onplaying=beganAutoplaying() loop id="foo"><source src="large-video-with-audio.mp4"></video>
    <br>
    <video id="bar"><source src="large-video-with-audio.mp4"></video>
</body>
<html>