I have literally read every stackoverflow thread regarding changing the video tag source dynamically via javascript in IE9, including the useful but not agreed upon posts he
Great news, I found a true solution to switching/changing videos in HTML5 video tags via JavaScript without using the annoying hack I tried to explain! It's unbelievably simple and it just took a LOT of experimenting with IE. Below is the code in its simplest form to work in IE:
<html>
<body>
<video id='videoPlayer' width="320" height="240" controls="controls">
<source id='mp4Source' src="movie.mp4" type="video/mp4" />
<source id='oggSource' src="movie.ogg" type="video/ogg" />
</video>
<!-- You MUST give your sources tags individual ID's for the solution to work. -->
<script>
var player = document.getElementById('videoPlayer');
var mp4Vid = document.getElementById('mp4Source');
player.pause();
// Now simply set the 'src' property of the mp4Vid variable!!!!
mp4Vid.src = "/pathTo/newVideo.mp4";
player.load();
player.play();
</script>
</body>
</html>
And there you have it. Unbelievably simple -- tested and working in IE8, and IE9... If you are having any problems, please let me know.