title: How to access Facebook voice messages in a Bot?
body: <p>I'm currently trying to get the audio/voice messages from user into my bot.
  I'm using MS Bot Framework and I know voice messages are stored as an attachment and in the format "video/mp4" according to this post, <a href="https://stackoverflow.com/questions/40918731/can-bot-framework-handle-facebook-audio-message">Can Bot Framework handle Facebook Audio Message</a>. But I don't know how to access the attachment the right way.</p>
  
  <pre><code>var sound = activity.Attachments?.FirstOrDefault(a =&gt; a.ContentType.Equals("video/mp4"));
  
  if (sound != null) {
                      await context.PostAsync("I have received sound");
                      context.Done(context);
                  }
  </code></pre>
  
  <p>Unfortunately <code>sound</code> was always empty.</p>
  
  <p>So how can I access the sound attachment the right way? And what Nuget-Package would you recommend for encoding it to "audio/wave" format for the Bing Speech Api?</p>