Force field for the output video frame.

The setfield filter marks the interlace type field for the output frames. It does not change the input frame, but only sets the corresponding property, which affects how the frame is treated by following filters (e.g. fieldorder or yadif).

It accepts a string parameter, which can assume the following values:

auto

Keep the same field property.

bff

Mark the frame as bottom-field-first.

tff

Mark the frame as top-field-first.

prog

Mark the frame as progressive.