Here is a simple approach which triggers when the video ends.
<html>
<body>
<video id="myVideo" controls="controls">
<source src="video.mp4" type="video/mp4">
etc ...
</video>
</body>
<script type='text/javascript'>
document.getElementById('myVideo').addEventListener('ended', function(e) {
alert('The End');
})
</script>
</html>
In the 'EventListener' line substitute the word 'ended' with 'pause' or 'play' to capture those events as well.