A straightforward way of doing this:
<script>
var video = document.querySelector('video');
video.addEventListener('ended', function() {
video.load();
});
</script>
Indeed when changing the src of a video tag you implicitly call a load() on it.
This method has the caveat to request the media URL again and depending on caching settings it may re-download the full-length media resource causing unnecessary network/CPU usage for the client.
A more appropriate way to solve this issue is to use an overlay image/div on top the video tag and to hide it when video starts. When the ended event fires just show the overlay image again.