Filter xmedian
  Pick median pixels from several video inputs.
    slice threading supported
    Inputs:
        dynamic (depending on the options)
    Outputs:
       #0: default (video)
xmedian AVOptions:
  inputs            <int>        ..FV..... set number of inputs (from 3 to 255) (default 3)
  planes            <int>        ..FV..... set planes to filter (from 0 to 15) (default 15)


