[FFmpeg-user] stroboscope effect

[Moritz Barsnick]

On Mon, Sep 08, 2014 at 03:16:52 +0200, Gerion Entrup wrote:
> ffplay -f lavfi -i color=black:s=512x512 -vf
> "framestep=3,drawbox=x=0:y=0:w=512:h=512:color=white:t=500"

framestep selects every n-th frame and passes that on to the following
filter chain, which is not what you want. You want the filter to
_apply_ only every 3rd frame. "drawbox" supports the "enable" option
for this. This works for me:

ffplay -f lavfi -i "color=black:s=512x512" -vf "drawbox=x=0:y=0:w=256:h=256:color=white:t=500:enable=not(mod(n\,3))"

Regards,
Moritz