fix constraint violation: libavformat is not allowed to modify state of caller, including rng state

Originally committed as revision 5249 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/rtp.c

@@ -532,9 +532,9 @@ static int rtp_write_header(AVFormatContext *s1)
         payload_type = RTP_PT_PRIVATE; /* private payload type */
     s->payload_type = payload_type;
 
-    s->base_timestamp = random();
+    s->base_timestamp = 0; /* FIXME: was random(), what should this be? */
     s->timestamp = s->base_timestamp;
-    s->ssrc = random();
+    s->ssrc = 0; /* FIXME: was random(), what should this be? */
     s->first_packet = 1;
 
     max_packet_size = url_fget_max_packet_size(&s1->pb);