Construct the media object and create its streams.
Implementations should create the needed gstreamer elements and add them to the result object. No state changes should be performed on them yet.
One or more GstRTSPStream objects should be created from the result with gst_rtsp_media_create_stream ().
After the media is constructed, it can be configured and then prepared with gst_rtsp_media_prepare ().
The returned media will be locked and must be unlocked afterwards.
the url used
a new Media if the media could be prepared.