How to receive a multicast stream with a sap name?

[tiantao]

I know the client use command like vlc udp://@239.20.30.40 can receive a multicast stream. but how to receive a multicast stream with a sap channel name?
if in the server, i use
vlc -vvv gigi.mpg :sout=#duplicate{dst=std{access=udp,mux=ts,url=239.20.30.40:1234,sap="a"}} ;
in the client, the command vlc -vvv --extraintf sap, can open the vlc, if choose playlist can see the 'a' channel. double click it, can receive the stream.
but how can do it automatic?
I want to type a single command like
vlc udp://@239.20.30.40{sap="a"} or something like this to receive the stream immedialy. how can I make it?
Thank you for seeing my question, I am waiting your reply.
Thank you!