[HELP] Converting 25p to 25i using Low Pass Filter in ffmpeg

[Selur]

will result in a 12,5fps Quicktime with separate odd and even fields in one frame.

oh, I overlooked that you wanted 25i.
try adding "-r 25"

Buw how to setup the flag (complex_filter, cvlpf)?

Assuming you are referring to tinterlace:

-vf tinterlace=mode=4:flags=cvlpf

Cu Selur

Ps.: if that doesn't work you probably have to 1st convert 25p to 50p and then convert it to 25i.