There is 2 new deinterlacing modes: "Yadif" and "Yadif (2x)".
"Yadif (2x)" doubles the frame rate, whereas "Yadif" throws away one field.

yadif.h comes from vf_yadif.c (GPLv2+) from MPayer project. I have stripped it
a bit but let the functions unmodified for easier maintainance.