title: iframe can't find YouTube videos in HTML
body: <p>For a website I am designing for an assignment about kids films and I thought I would put an iframe in to show the trailer from a YouTube video. This is the code I used (just with a test video);</p>
  
  <pre><code>&lt;iframe width="560" height="315" src="//www.youtube.com/embed/xxMcViTf7KU" frameborder="0" allowfullscreen&gt;This is the test iframe&lt;/iframe&gt;
  </code></pre>
  
  <p>The result is the page begins to load, then a box comes up saying 'file or directory not found'. As far as I am aware, the code is all correct. I don't understand what's wrong.</p>
  
  <p>Any help would be greatly appreciated, thank you!</p>