well, fragmentation happens on the IP layer.
TCP doesn’t “fragment”, it’s a stream where the granularity is a single byte. UDP can’t fragment, it’s unrelated datagrams of upto 64K size.
Python is okay with binding to the empty string, which is equivalent to all interfaces.
you can use nonblocking sockets but why bother? just use any method for polling (select, poll, epoll, whatever). the cv.waitKey sets the pace because it contains implicit delays.
that is insufficient.
you need to debug your code. learn to use python’s debugger, or at least use printlining (“printf-debugging”) to follow the flow of execution and observe the state.
your code looks like it should work in principle. perhaps your network/OS firewall just drops the packets or the packets are caught by a NAT or whatever.
above all that: your problem doesn’t involve OpenCV except for the attempt to decode some data and show it in a GUI. it doesn’t even involve gstreamer (thread was tagged as “gstreamer”). it’s just python and sockets. please bring your issue to a forum that deals with general programming education.