Autoplay HTML5 Video with preload="none" and JavaScript
<video id="autoplay" preload="none" muted playsinline controls>
<source src="video.mp4" type="video/mp4">
<source src="video.webm" type="video/webm">
</video>
<script>
document.getElementById('autoplay').play();
</script>
Video source: Sintel, the Durian Open Movie Project