phase vocoder part 1 by Dudas and Lippe (Jean Francois)….

Hi all, Hi Jean-Francois,
I do refer to the phase vocoder patch by Dudas and Lippe. Another question, pleae. I don’t understand why with an FFT overlap of 4 we get a velocity 4 time faster (the reason because we need an input coefficient of 0.25)…
I know what is the overlap but I don’t know why we get a velocity 4 time faster….
Could you please help me.
Thanks
fv