How to get SDP file for any RTSP file?

How to get SDP file for any RTSP file?
RTSP response will have the SDP description
if we are having rtsp URL, we can open it with Quick time Player and at the same time, we can open the Ethereal to capture the net logs.
RTSP response RTSP/1.1 200 OK will have a SDP description.
Even with this SDP description and save it into SDP file and open it in Quick time, we are able to play it in Quick time