sfmf applies a median filter on the first dimension of the input.
The size of the filter window is controlled by nfw= parameter. The following example from tccs/medianfilter/dragon shows field seismic data before and after 11-point (nfw=11) median filtering combined with bandpass filtering. 
For time-variant median filtering, see sftvmf. To simply output the median of the first axis, use sfmedian.