Gstreamer 1.2.3 dont work with udp multicast in Windows 7. Gstreamer does not transmit or receive multicast packets. 
I have scanned ports by Wireshark, but there is not packets sended from Gstreamer. There is no log output with debug option GST_DEBUG=udp*:6 on sender side(server side). Pipeline on sender side  
gst-launch-1.0 --gst-debug=udp*:6  videotestsrc ! video/x-raw,format=RGB, width=320, height=240, framerate=30/1! videoconvert ! avenc_mpeg4 ! rtpmp4vpay config-interval=1 ! udpsink host=224.1.1.1 port=5004 auto-multicast=true

Pipeline of receiver side
gst-launch-1.0 udpsrc uri=udp://224.1.1.1:5004 caps="application/x-rtp, media=(string)video" ! rtpmp4vdepay ! avdec_mpeg4 ! videoconvert ! autovideosink

Debug output of receive side with option --gst-debug=udp*:6 is
gst-launch-1.0  --gst-debug=udp*:6 udpsrc uri=udp://224
1.1.1:5004 caps="application/x-rtp, media=(string)video" ! rtpmp4vdepay ! avdec
mpeg4 ! videoconvert ! autovideosink
Setting pipeline to PAUSED ...
0:00:00.479354698  3744   07EE9C40 DEBUG                 udpsrc gstudpsrc.c:824
gst_udpsrc_start:<udpsrc0> allocating socket for 224.1.1.1:5004
0:00:00.484223673  3744   07EE9C40 DEBUG                 udpsrc gstudpsrc.c:794
gst_udpsrc_resolve:<udpsrc0> IP address for host 224.1.1.1 is 224.1.1.1
0:00:00.487240744  3744   07EE9C40 DEBUG                 udpsrc gstudpsrc.c:837
gst_udpsrc_start:<udpsrc0> got socket 080051D8
0:00:00.490789888  3744   07EE9C40 DEBUG                 udpsrc gstudpsrc.c:844
gst_udpsrc_start:<udpsrc0> binding on port 5004
0:00:00.493673313  3744   07EE9C40 INFO                  udpsrc gstudpsrc.c:912
gst_udpsrc_start:<udpsrc0> have udp buffer of 8192 bytes
0:00:00.496406778  3744   07EE9C40 DEBUG                 udpsrc gstudpsrc.c:965
gst_udpsrc_start:<udpsrc0> joining multicast group 224.1.1.1
0:00:00.498551072  3744   07EE9C40 DEBUG                 udpsrc gstudpsrc.c:985
gst_udpsrc_start:<udpsrc0> bound, on port 5004
Pipeline is live and does not need PREROLL ...
Setting pipeline to PLAYING ...
0:00:00.503949925  3744   07EE9C40 LOG                   udpsrc gstudpsrc.c:105
:gst_udpsrc_unlock_stop:<udpsrc0> No longer flushing
New clock: GstSystemClock
0:00:00.506317904  3744   07EE3EE8 LOG                   udpsrc gstudpsrc.c:421
gst_udpsrc_create:<udpsrc0> doing select, timeout 18446744073709551615