Filter lagfun
  Slowly update darker pixels.
    slice threading supported
    Inputs:
       #0: default (video)
    Outputs:
       #0: default (video)
lagfun AVOptions:
  decay             <float>      ..FV..... set decay (from 0 to 1) (default 0.95)
  planes            <flags>      ..FV..... set what planes to filter (default F)


