How to apply a very basic SOLA algorithm to an audio signal (without autocorrelation)

Hi everyone, i need some help and guidance please with something. i must apply the SOLA (Synchronous Overlap and Add)) algorithm to an audio song, for stretch it or slow down it. I've been trying to do something for quite a few days and I'm about to lose my mind. I just need some orientation to know how to apply a sliding window in the time domain over the audio signal to cut it into segments (ei 50ms), and then, overlap them in such a way to achieve the accelerated or slowed down effect without changing the tone. The problem is the sliding window has to be something like a trapezoid just like the image that i attached. My DSP had some "troubles" to explain these concepts so I am quite confused on how to do it. Could anyone help me please? i'm pretty noob using matlab yet ): Thanks!

PS: My writing in English isn't very good yet, I apologize if something wasn't understood.