How do I make a webm video file play?

I've got one to appear by placing

var video = $("<video/>");

sym.$("vcontainer").append(video);

video.attr('id','video1');

var webm = $("<source/>");

video.append(webm);

webm.attr('src','big_buck_bunny.webm');

webm.attr('type',"video/webm");

on compositionReady, where vcontainer is a div on the stage. I can see the first frame.

I've also added a div to act as a play button. On its click handler I've added

sym.$("video1").play();

but it doesn't do anything. How do I control the video?