sdp: Ignore RTCP packets when autodetecting RTP streams

The rtp demuxer which listens for RTP packets and detects the
RTP payload type will currently get confused if the first packet
received is an RTCP packet. Thus ignore such packets.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/rtsp.c

@@ -1927,6 +1927,9 @@ static int rtp_read_header(AVFormatContext *s)
             continue;
         }
 
+        if (recvbuf[1] >= RTCP_SR && recvbuf[1] <= RTCP_APP)
+            continue;
+
         payload_type = recvbuf[1] & 0x7f;
         break;
     }