A .webm file is for video.

Embed one like so in HTML?

<div style="width:400px;">
   <video autoplay="" loop="" muted=""
         poster="http://i2.cdn.turner.com/cnn/2015/images/10/14/handshake2.jpg"
         style="border: 0; height: auto; width: 100%;">
      <source src="http://i.cdn.turner.com/cnn/.
            e/interactive/videos/2015/10/14/handshake2.webm" type="video/webm">
      <source src="http://i.cdn.turner.com/cnn/.
            e/interactive/videos/2015/10/14/handshake2.mp4" type="video/mp4">
      <img src="http://i2.cdn.turner.com/cnn/2015/images/10/14/handshake2.jpg"
            data-demand-load="loaded">
   </video>
<div>