title: Why do some WebM videos seamlessly loop and others do not?
body: <p>One thing I have noticed is that if you had a video inserted into a webpage like so:</p>
  
  <pre><code>&lt;video loop src='video.webm'&gt;&lt;/video&gt;
  </code></pre>
  
  <p>On videos that have sound, when the video is over and started back to the beginning, there is a short delay.</p>
  
  <p>It also seems that if the WebM has no audio stream in the container, the video loops seamlessly, with no delay between end and beginning.</p>
  
  <p>Why is that?</p>