I can not find answer to this question from documentation.
my sincere apologies, sometimes eyes see what you want them to see
RSTP is not same as RTSP, nowhere near.
ok as per my knowledge, RTSP (streaming protocol) involves client server communication on TCP/UDP port 554 and some other fundamentals where all the communication happens between client & server and router has to do what it meant to do i.e. route traffic between server & client.
It should be like any other application level protocol (http, ftp) where you need not to see if router support this protocol until unless you block traffic with some ACL or router act as mediator between server & client (proxy kind of thing).
I will see if I can get you some specific source of information. In the meantime, you may get some expert opinion from netpro community.