title: How to get list of available youtube subtitles from youtube-dl python api alongside other video informations
body: <p>I have been using youtube-dl python Api for getting information about videos on youtube. here is part of my code I used to retrieve video information.</p>
  
  <pre><code>ydl_opts = {'simulate' : True, 'print_json': True, 'extract_flat': True}
  ydl = youtube_dl.YoutubeDL(ydl_opts);
  meta = ydl.extract_info('https://www.youtube.com/watch?v=YuOBzWF0Aws');
  </code></pre>
  
  <p>here <code>meta</code> contains video information in json format. <br/>
  Now I want to get list of available video subtitles alongside video information I tried with the following code:</p>
  
  <pre><code>ydl_opts = {'simulate' : True, 'print_json': True, 'extract_flat': True, 'listsubtitles': True}
  ydl = youtube_dl.YoutubeDL(ydl_opts);
  meta = ydl.extract_info('https://www.youtube.com/watch?v=YuOBzWF0Aws');
  </code></pre>
  
  <p>but this code would just print the available subtitles in stdout and <code>meta</code> is empty.<br/>
  now I have two problems.<br />
  1- is there a way to get list of available subtitles in array or json format? <br/>
  2- how to get list of subtitles alongside video information in <strong>one request</strong>?</p>