avformat/rtpproto: when local rtp port and local rtcp port are not specified, try to make two successive ports and retry 3 times when failed

some video players on Android will not send udp hole punching messages if the rtcp port and rtp port are not two successive integers.
So, if the video player is behind NAT, it could not receive and rtp messages via udp

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/rtpproto.c

@@ -281,6 +281,7 @@ static int rtp_open(URLContext *h, const char *uri, int flags)
     char buf[1024];
     char path[1024];
     const char *p;
+    int i, max_retry_count = 3;
 
     av_url_split(NULL, 0, NULL, 0, hostname, sizeof(hostname), &rtp_port,
                  path, sizeof(path), uri);
@@ -328,19 +329,35 @@ static int rtp_open(URLContext *h, const char *uri, int flags)
         }
     }
 
-    build_udp_url(buf, sizeof(buf),
-                  hostname, rtp_port, local_rtp_port, ttl, max_packet_size,
-                  connect, include_sources, exclude_sources);
-    if (ffurl_open(&s->rtp_hd, buf, flags, &h->interrupt_callback, NULL) < 0)
-        goto fail;
-    if (local_rtp_port>=0 && local_rtcp_port<0)
-        local_rtcp_port = ff_udp_get_local_port(s->rtp_hd) + 1;
-
-    build_udp_url(buf, sizeof(buf),
-                  hostname, rtcp_port, local_rtcp_port, ttl, max_packet_size,
-                  connect, include_sources, exclude_sources);
-    if (ffurl_open(&s->rtcp_hd, buf, flags, &h->interrupt_callback, NULL) < 0)
-        goto fail;
+    for (i = 0;i < max_retry_count;i++) {
+        build_udp_url(buf, sizeof(buf),
+                      hostname, rtp_port, local_rtp_port, ttl, max_packet_size,
+                      connect, include_sources, exclude_sources);
+        if (ffurl_open(&s->rtp_hd, buf, flags, &h->interrupt_callback, NULL) < 0)
+            goto fail;
+        local_rtp_port = ff_udp_get_local_port(s->rtp_hd);
+        if(local_rtp_port == 65535) {
+            local_rtp_port = -1;
+            continue;
+        }
+        if (local_rtcp_port<0) {
+            local_rtcp_port = local_rtp_port + 1;
+            build_udp_url(buf, sizeof(buf),
+                          hostname, rtcp_port, local_rtcp_port, ttl, max_packet_size,
+                          connect, include_sources, exclude_sources);
+            if (ffurl_open(&s->rtcp_hd, buf, flags, &h->interrupt_callback, NULL) < 0) {
+                local_rtp_port = local_rtcp_port = -1;
+                continue;
+            }
+            break;
+        }
+        build_udp_url(buf, sizeof(buf),
+                      hostname, rtcp_port, local_rtcp_port, ttl, max_packet_size,
+                      connect, include_sources, exclude_sources);
+        if (ffurl_open(&s->rtcp_hd, buf, flags, &h->interrupt_callback, NULL) < 0)
+            goto fail;
+        break;
+    }
 
     /* just to ease handle access. XXX: need to suppress direct handle
        access */