Hello,
as far as the streaming with vlc is concerned,
this will probably answer your questions. I personally use RTP and the multicast address of 239.255.100.100 and it works perfectly.
If you want the multicast traffic to cross vlans, you will need to configure a multicast routing protocol. The EX switches support PIM-SM.
If you would like more information and examples on this, then I would highly recommend the chapter on multicast in the JUNOS Enterprise Routing book.
BR,
MarkG