title: Unable to receive RTP payload type 96 without an SDP file describing it
body: <p>How can I use SDP files in iOS FFmpeg? I've tried this:</p>
  
  <pre><code>char *url = "rtp://127.0.0.1:1234"; 
  AVFormatContext *oc = NULL; 
  avformat_open_input(&amp;oc, url, NULL , NULL); 
  </code></pre>
  
  <p>But I get the following error: </p>
  
  <blockquote>
    <p>[rtp @ 028568e0] Unable to receive RTP payload type 96 without an SDP file 
        describing it.  </p>
  </blockquote>