gr-strf is an out-of-tree GNURADIO module to produce time-stamped waterfall files. It will duplicate the functionality of the rffft tool from https://github.com/cbassa/strf.
gr-strf is based on the SatNOGS waterfall sink from gr-satnogs (https://gitlab.com/librespacefoundation/satnogs/gr-satnogs).