The PAL analog video always runs at 25 frames per second. The reduced video rate is achieved by duplicating frames. The analog video is usually the easiest to use in a UAV / drone / quadcopter application because of the availability of analog video downlink modules. The digital video on reduced video rate cameras does run at the reduced rate, but some custom interfacing is usually need to pass it into processing or transmission hardware.
Information about Tau2 video operation and format can be found in the product specification and electrical IDD documents here: www.flir.com/cvs/cores/view/?id=54717&collectionid=612&col=54721