Impact of the WSOLA analysis increment on the time stretching factor WSOLA, basically, is the same as OLA but with a dynamic hop size. That part is clear to me. What is not so clear is the following: The stretching factor is determined by alpha = Hs / Ha and WSOLA uses a small increment, obtained through cross-correlation, to determine where the next input frame will be extracted. If that's the case, doesn't that small increment introduce a deviation between the requested alpha and the real one? After all, that increment determines a new analysis hop size, Ha' = Ha + incr, meaning that, if we maintain the same synthesis hop size, the alpha will change.
Yes, there can be jitter between the requested alpha and the one provided by WSOLA; but that jitter will average out over the long run, and the peak jitter is bounded by on the order of twice the lowest frequency (half the longest period) accepted by the autocorrelation algorithm.