source code about the variant folder

I am using the rtsp for streamning my usb camera by using the UVC class. And the folder variants contains some files with lib_xxx.a. As I want to add rtcp to my video stream, I need to know how the rtsp is impelemented with the source code of the lib files.
Any addvise?
I am really appreciate that any instructions from the usb camera to the rtsp server will be available!