title: Error with audio in sr_freecap captcha extension
body: <p>I implemented sr_freecap extension in form. All works fine except the audio output. Audio works in Safari browser but not in Firefox or Chrome. In Chrome i get the following error in the console:</p>
  <p>Uncaught (in promise) DOMException: Failed to load because no supported source was found.</p>
  <p>[EDIT]</p>
  <p>I made a few more attempts and found that only the first call does result in this error. Let me try to explain it more accurate:</p>
  <ul>
  <li>page is called in browser</li>
  <li>clicks on the audio symbol in the captcha results in this error</li>
  <li>reload the captcha (get a new captcha image)</li>
  <li>clicks on the audio symbol results in playing the correct audio captcha without any error</li>
  </ul>
  <p>I analyzed the network traffic for the first click (error) and the click after refreshing the captcha (no error). There is only one difference: the result header Content-Length for the first click is 0. So it seems that the audio file  of the first click is simply empty.</p>
  <p>In Safari every click results in a valid audio file.</p>
  <p>Any idea what is wrong here?
  Thanks!</p>