you can use ffplay, VLC or other players to get the original fps. you also can use the following comamnd-line to test the original fps. please refer to this topic.
gst-launch-1.0 rtspsrc location=rtsp://127.0.0.1:8554/test ! rtph264depay ! h264parse ! decodebin ! fpsdisplaysink video-sink=fakesink text-overlay=false sync=false -v |grep current