Perform various types of temporal field interlacing.

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

The filter accepts the following options:

mode

Specify the mode of the interlacing. This option can also be specified as a value alone. See below for a list of values for this option.

Available values are:

merge, 0

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

drop_odd, 1

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

drop_even, 2

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

pad, 3

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

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 frame rate.

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 frame rate.

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.

flags

Specify flags influencing the filter process.

Available value for flags is:

low_pass_filter, vlfp

Enable vertical low-pass filtering in the filter. Vertical low-pass filtering is required when creating an interlaced destination from a progressive source which contains high-frequency vertical detail. Filtering will reduce interlace ’twitter’ and Moire patterning.

Vertical low-pass filtering can only be enabled for modeinterleave_top and interleave_bottom.