title: Tell RMarkdown to not contain videos
body: <p>RMarkdown is very useful and I build html documents containing both figures generated by R and some video links which I add straight through html as follows:</p>
  
  <pre><code>&lt;video controls width="1000" height="600"  poster="linktoposter.jpg"&gt;
  &lt;source src="linkto.webm" type="video/webm"&gt;
  &lt;source src="http://linkto.mp4" type="video/mp4"&gt;
  &lt;/video&gt;   
  </code></pre>
  
  <p>This works absolutely fine except that RMarkdown downloads the video and embeds it in the html file.<br>
  When there are a few videos in the same document the html produced can reach 100s of megabytes in size.</p>
  
  <p>I'd like to turn off the <code>self-contained</code> option but only for videos not for the charts R generates. Is there a way to do that? An html tag or class option perhaps?</p>