[FFmpeg-user] How to drop every Nth frame?

[Andrey Aleksandrovich]

>>> This interested me because I am trying inverse telecine on 30 fps source
>>> (I normally work on 60 fps telecined 1080i sources). This was Carl Eugen's
>>> first reply to the discussion:

My situation is that I need to sync a-v (expanding desync, 0 at start
and 14 sec at the end).
The audio filter 'atempo' doesn't help because it accepts only 3
numbers after coma (0.XXX). In my case it's limits are: 0.998 (-3.3
sec desync at the end) and 0.997 (+7.3 sec desync at the end).
So I think I can make it by contraction of video (dropping frames with
changing duration).

Maybe you can suggest another way...