[FFmpeg-user] Keep vfr and original pts

[Wolfgang Hugemann]

I have a vfr mp4 video from a private security cam with a very specific
pts pattern. The duration of the frames is
80-80-40-80-80-40-80-80-40-... ms.

I would like to hand this video to others as a demonstration of vfr
video, but have to blur it in order to preserve privacy.

I tried something like

ffmpeg -i in.mp4 -vf boxblur=10:1 -vsync 2 -copyts blur.mp4

which results in cfr video whith 15 fps.

ffmpeg -i in.mp4 -vf boxblur=10:1 -r 25 -vsync 2 -copyts blur.mp4
or
ffmpeg -i in.mp4 -vf boxblur=10:1 -r 25 -vsync 0 -copyts blur.mp4

generates vfr and kind of keeps the pts, but inserts additional frames.

What goes wrong over here?

Regards
Wolfgang Hugemann