Interestingly, it does not work for me (42.1). I get "We think this page has embedded the HTML5 player, as seen below:" and a picture appears in the box, but when clicking to play the video I get "Sorry, you need Flash to play this."
What happened to me was first it said I needed to install flash, then after a short delay, it changed to "this content doesn't seem to be working".
You have to be opted in to html5 to test it. It says if you are on the right hand side. If you are not, it will use flash. You can clear out cookies and rerun to be opted in I think.