Index: libavformat/rtpproto.c
===================================================================
--- libavformat/rtpproto.c	(revision 21510)
+++ libavformat/rtpproto.c	(working copy)
@@ -188,9 +188,9 @@
 static int rtp_read(URLContext *h, uint8_t *buf, int size)
 {
     RTPContext *s = h->priv_data;
-    struct sockaddr_in from;
+	struct sockaddr from;
     socklen_t from_len;
-    int len, fd_max, n;
+    int len, fd_max, n, is_rtcp_packet;
     fd_set rfds;
 #if 0
     for(;;) {
@@ -216,8 +216,10 @@
         FD_SET(s->rtcp_fd, &rfds);
         n = select(fd_max + 1, &rfds, NULL, NULL, NULL);
         if (n > 0) {
+			is_rtcp_packet = 0;
             /* first try RTCP */
             if (FD_ISSET(s->rtcp_fd, &rfds)) {
+				is_rtcp_packet = 1;
                 from_len = sizeof(from);
                 len = recvfrom (s->rtcp_fd, buf, size, 0,
                                 (struct sockaddr *)&from, &from_len);
@@ -244,6 +246,14 @@
             }
         }
     }
+
+    /* If we have an appropriate registered callback, allow it to decide whether to drop this packet or not */
+    if (h->check_net_packet_callback != NULL) {
+        if (!(h->check_net_packet_callback(&from, buf, size))) {
+            av_log(NULL, AV_LOG_DEBUG, "Net packet callback check tells us to drop this packet, so we will.");
+            return AVERROR(EAGAIN);
+        }
+    }
 #endif
     return len;
 }
Index: libavformat/avformat.h
===================================================================
--- libavformat/avformat.h	(revision 21510)
+++ libavformat/avformat.h	(working copy)
@@ -683,6 +683,14 @@
      */
 #define RAW_PACKET_BUFFER_SIZE 2500000
     int raw_packet_buffer_remaining_size;
+
+    /**
+     * Callback called just after getting a packet but before returning
+     * for processing in demuxers dealing with data over a network; can
+     * be used to accept/reject packets based on eg. source address.
+	 * Return 0 to reject the packet, nonzero to accept it.
+     */
+    int (*check_net_packet_callback)(struct sockaddr *srcaddress, uint8_t *buf, int buflen);
 } AVFormatContext;
 
 typedef struct AVPacketList {
Index: libavformat/rtsp.c
===================================================================
--- libavformat/rtsp.c	(revision 21510)
+++ libavformat/rtsp.c	(working copy)
@@ -1808,6 +1808,7 @@
             err = AVERROR_INVALIDDATA;
             goto fail;
         }
+		rtsp_st->rtp_handle->check_net_packet_callback = s->check_net_packet_callback;
         if ((err = rtsp_open_transport_ctx(s, rtsp_st)))
             goto fail;
     }
Index: libavformat/Makefile
===================================================================
--- libavformat/Makefile	(revision 21510)
+++ libavformat/Makefile	(working copy)
@@ -3,7 +3,7 @@
 NAME = avformat
 FFLIBS = avcodec avutil
 
-HEADERS = avformat.h avio.h
+HEADERS = avformat.h avio.h network.h
 
 OBJS = allformats.o         \
        cutils.o             \
Index: libavformat/avio.h
===================================================================
--- libavformat/avio.h	(revision 21510)
+++ libavformat/avio.h	(working copy)
@@ -31,6 +31,7 @@
 #include <stdint.h>
 
 #include "libavutil/common.h"
+/* #include "libavformat/network.h" - jez bookmark */
 
 /* unbuffered I/O */
 
@@ -51,6 +52,13 @@
     int max_packet_size;  /**< if non zero, the stream is packetized with this max packet size */
     void *priv_data;
     char *filename; /**< specified URL */
+    /**
+     * Callback called just after getting a packet but before returning
+     * for processing in demuxers dealing with data over a network; can
+     * be used to accept/reject packets based on eg. source address.
+	 * Return 0 to reject the packet, nonzero to accept it.
+     */
+    int (*check_net_packet_callback)(struct sockaddr *srcaddress, uint8_t *buf, int buflen);
 } URLContext;
 
 typedef struct URLPollEntry {