@@ -446,6 +446,11 @@ set the UDP buffer size in bytes

 @item localport=@var{port}

 override the local UDP port to bind with

+@item localaddr=@var{addr}

+Choose the local IP address. This is useful e.g. if sending multicast

+and the host has multiple interfaces, where the user can choose

+which interface to send on by specifying the IP address of that interface.

+

 @item pkt_size=@var{size}

 set the size in bytes of UDP packets

@@ -29,6 +29,7 @@

 #include "avformat.h"

 #include "avio_internal.h"

 #include "libavutil/parseutils.h"

+#include "libavutil/avstring.h"

 #include <unistd.h>

 #include "internal.h"

 #include "network.h"

@@ -178,8 +179,8 @@ static int udp_set_url(struct sockaddr_storage *addr,

     return addr_len;

 }

-static int udp_socket_create(UDPContext *s,

-                             struct sockaddr_storage *addr, int *addr_len)

+static int udp_socket_create(UDPContext *s, struct sockaddr_storage *addr,

+                             int *addr_len, const char *localaddr)

 {

     int udp_fd = -1;

     struct addrinfo *res0 = NULL, *res = NULL;

@@ -187,7 +188,8 @@ static int udp_socket_create(UDPContext *s,

     if (((struct sockaddr *) &s->dest_addr)->sa_family)

         family = ((struct sockaddr *) &s->dest_addr)->sa_family;

-    res0 = udp_resolve_host(0, s->local_port, SOCK_DGRAM, family, AI_PASSIVE);

+    res0 = udp_resolve_host(localaddr[0] ? localaddr : NULL, s->local_port,

+                            SOCK_DGRAM, family, AI_PASSIVE);

     if (res0 == 0)

         goto fail;

     for (res = res0; res; res=res->ai_next) {

@@ -302,7 +304,7 @@ static int udp_get_file_handle(URLContext *h)

 /* return non zero if error */

 static int udp_open(URLContext *h, const char *uri, int flags)

 {

-    char hostname[1024];

+    char hostname[1024], localaddr[1024] = "";

     int port, udp_fd = -1, tmp, bind_ret = -1;

     UDPContext *s = NULL;

     int is_output;

@@ -350,6 +352,9 @@ static int udp_open(URLContext *h, const char *uri, int flags)

         if (av_find_info_tag(buf, sizeof(buf), "connect", p)) {

             s->is_connected = strtol(buf, NULL, 10);

         }

+        if (av_find_info_tag(buf, sizeof(buf), "localaddr", p)) {

+            av_strlcpy(localaddr, buf, sizeof(localaddr));

+        }

     }

     /* fill the dest addr */

@@ -367,7 +372,7 @@ static int udp_open(URLContext *h, const char *uri, int flags)

     if ((s->is_multicast || !s->local_port) && (h->flags & AVIO_FLAG_READ))

         s->local_port = port;

-    udp_fd = udp_socket_create(s, &my_addr, &len);

+    udp_fd = udp_socket_create(s, &my_addr, &len, localaddr);

     if (udp_fd < 0)

         goto fail;