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

[Wolfgang Hugemann]

> You mentioned that you wished to extract these selected frames as
> images. As long as you use -vsync 0, there will be no frame duplication,
> and the result is the extraction of every 5th frame. 

Sorry, you are right. And thanks for "-vsync 0", which is decisive, also
when dumping the frames as JPEGs.

Your suggested code does the trick.

Wolfgang Hugemann