Filter fieldorder
  Set the field order.
    Inputs:
       #0: default (video)
    Outputs:
       #0: default (video)
fieldorder AVOptions:
  order             <int>        ..FV..... output field order (from 0 to 1) (default tff)
     bff             0            ..FV..... bottom field first
     tff             1            ..FV..... top field first

This filter has support for timeline through the 'enable' option.

