title: Unable to record window with ffmpeg
body: <p>I am trying to video-record a browser window with <code>ffmpeg</code>. The browser window is a firefox window with title <code>OpenID Connect Server - Log In</code>, so I tried the following command (based on the suggestion given <a href="https://stackoverflow.com/questions/25396784/how-to-record-a-specific-window-using-ffmpeg">here</a>):</p>
  
  <pre><code>ffmpeg -f x11grab -framerate 30 -i title="OpenID Connect Server - Log In" -b:v 3M  germ.flv
  </code></pre>
  
  <p>but I get an error</p>
  
  <pre><code>[x11grab @ 0x1fd7980] Cannot open display title=OpenID Connect Server - Log In, error 5.
  title=OpenID Connect Server - Log In: Input/output error
  </code></pre>
  
  <p>Anything I am missing?</p>
  
  <p><strong>Addition:</strong></p>
  
  <ol>
  <li>I need a tool to be used on command line (starting and stopping recording).</li>
  <li>The goal is to record selenium tests from a window. But I need to run like 50 tests, which all open and close their own firefox window. Therefore I need the command line ability.  </li>
  </ol>