[FFmpeg-devel] Quick Patch for Multicast UDP Receive on macOS

[ffmpeg at gallery.co.uk]

Hi Folks.

New here, so apologies if this is not how its done,  but I have a tiny patch to fix a fundamental flaw in FFMPEG on macOS.

The Problem:  
-------------------
On macOS Try to run 2 copies of FFMPEG each consuming an RTP Multicast which are on *different* multicast addresses - but the *same* port.
The second copy will fail with a bind error and possibly a crash.

The Solution:
------------------
Very simple - on macOS you need to use SO_REUSEPORT as well as SO_REUSEADDR to avoid this sort of issue.

Thanks

Mark Gilbert
CTO: Gallery SIENNA.



PATCH FOLLOWS:
--------------------------



--- /Users/mark/Downloads/udpORIG.c	2018-08-16 15:39:21.000000000 +0100
+++ /Users/mark/Downloads/udp.c	2018-08-16 15:40:55.000000000 +0100
@@ -828,7 +828,11 @@
        s->reuse_socket = 1;
        if (setsockopt (udp_fd, SOL_SOCKET, SO_REUSEADDR, &(s->reuse_socket), sizeof(s->reuse_socket)) != 0)
            goto fail;
-    }
+  #ifdef __APPLE__  // MacOS/X requires an additional call 
+        if (setsockopt (udp_fd, SOL_SOCKET, SO_REUSEPORT, &(s->reuse_socket), sizeof(s->reuse_socket)) != 0)
+            goto fail;
+  #endif
+      }

    if (s->is_broadcast) {
#ifdef SO_BROADCAST