UDP multicast on iOS with WWAN turned on

[Dries Langsweirdt]

Hello,

I'm developing an iOS gstreamer application which essentially receives 
and visualizes an UDP multicast h264 stream. Everything works as 
expected, until Mobile network > Mobile data is turned on in the 
settings app on an iOS device with a SIM card. As soon as WWAN traffic 
is possible, no UDP packages are received by the gstreamer pipeline any 
longer (and as such no video displayed).

I have a separate application (no gstreamer involved), which creates an 
UDP socket listening on the same multicast address and port as the 
pipeline. In this application, turning the mobile data on or off has no 
influence on receiving UDP packages over WIFI. As such, I know this is 
not a limitation of the hardware or operating system. This has been 
confirmed to me by an Apple engineer. Furthermore, the Bonjour protocol 
is using UDP multicast as well independent of the mobile data status.

This is the pipeline I'm using:
udpsrc multicast-iface=en0 address=224.1.1.1 port=5004
     ! application/x-rtp, media=(string)video, clock-rate=(int)90000, ....
     ! rtpjitterbuffer latency=400
     ! rtph264depay ! h264parse ! vtdec ! videoconvert
     ! autovideosink

and I'm currently on gstreamer 1.10.2, iOS 9 and 10.

I have looked at the code in gstreamer (gstudpsrc.c > gst_udpsrc_open) 
and glib (gsocket.c > g_socket_multicast_group_operation) where the 
socket related operations are preformed, but don't see anything 
obviously odd at first sight.

I would like to know if I'm looking at an application specific problem 
or a general gstreamer problem, so if someone could confirm or 
de-confirm this behavior that would be great. Any suggestions as to how 
to proceed are greatly appreciated.

Thanks a lot.
-- 

Kind Regards,
Dries Langsweirdt