Explore the CameraStreamResolution sample, it shows how to get the resolution of an image.
You will have to understand that the information is for one image, resolution and also frame rate can change from one second to the next governed by rules or events.
As a consequence the only way to get the framerate is to retrieve images for a period and do a count.
If using XProtect Corporate and Expert you can with the Config API read the camera settings, under the assumptions that the user does not have any rules changing the settings this could be used as an alternative approach.