how to get SDP information from the Lua

edit

I want to using LUA get SDP information... want to get the Media Port 1234 and decode this port as RTCP

as I know I can using below code to decode 1234 port as RTCP but how can I get the 1234 this port from the SDP?

do
    local lee_port_table = DissectorTable.get("udp.port")
    local rtcp_dissector = Dissector.get("rtcp")
    lee_port_table:add(1234,rtcp_dissector)
end

                Media Description, name and address (m): application 1234 udp MCPTT
                    Media Type: application
                    Media Port: 1234
                    Media Protocol: udp
                    Media Format: MCPTT

is there anybody can help to show me some example code?

Regards