[FFmpeg-user] Reducing frame rate without reencoding

[Ronald F. Guilmette]

Apologies if this is an FAQ.

I have a video with a fixed frame rate of 59.940 fps.  Some of my devices
don't cope with this very well.  Thus, I'd like to convert the video to
one with exactly half the frame rate (29.970), but preferably without
doing any reencoding, e.g. just by stripping away every odd numbered
frame (or every even numbered one).

Is there a way to do this with ffmpeg, and if so, what is the command
line to do it?