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                          ..FV.... bottom field first
     tff                          ..FV.... top field first

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

