With the above; within the HTML
I had the same objective, and found a solution by using jQuery to reset the source of the video to itself on ended. Now I get my animated gif poster before and after play. Here is a simple javascript play function and the jQuery code.
function play()
{
movie_ID.play();
$(document).ready(function(){
$("#movie_ID").bind("ended", function() {
$('#movie_ID').attr('src', 'movie_ID.src');
});
});
}