Perform various types of temporal field interlacing.

Frames are counted starting from 1, so the first input frame is considered odd.

This filter accepts a single parameter specifying the mode. Available modes are:

merge, 0

Move odd frames into the upper field, even into the lower field, generating a double height frame at half framerate.

drop_odd, 1

Only output even frames, odd frames are dropped, generating a frame with unchanged height at half framerate.

drop_even, 2

Only output odd frames, even frames are dropped, generating a frame with unchanged height at half framerate.

pad, 3

Expand each frame to full height, but pad alternate lines with black, generating a frame with double height at the same input framerate.

interleave_top, 4

Interleave the upper field from odd frames with the lower field from even frames, generating a frame with unchanged height at half framerate.

interleave_bottom, 5

Interleave the lower field from odd frames with the upper field from even frames, generating a frame with unchanged height at half framerate.

interlacex2, 6

Double frame rate with unchanged height. Frames are inserted each containing the second temporal field from the previous input frame and the first temporal field from the next input frame. This mode relies on the top_field_first flag. Useful for interlaced video displays with no field synchronisation.

Numeric values are deprecated but are accepted for backward compatibility reasons.

Default mode is merge.