[FFmpeg-user] Treating video frame-based instead of time-based

[Wolfgang Hugemann]

> As Carl mentioned, the select filter with an appropriate expression will
> do this e.g.  select='not(mod(n-1,5))' to select every 5th frame. Frame
> count begins with 0.

The select filter keeps the framerate, such that the above code will
show every 5th frame for a 5 frame time interval. However this approach
may help to control rounding errors when using the fps filter.

Wolfgang Hugemann