For a school's project, I am programming a standard phase vocoder for time 
compression/expansion of digital audio. The audiodata is broken up in 
frames, each frame is multiplied by a window function (in my case a 
Hann-window) and the result is transformed into frequency-domain by FFT.

Now because the frames overlap each other, I was wondering if it's possible 
to optimize this computation. For example, I am using an FFT/window size of 
4096 and a frame hopsize of 64.
So strictly speaking there are only 64 "new" samples per new frame.

Also I noticed a standard implementation gives incorrect beginning and 
endings of the processed data, with a fade-in respectively fade-out due to 
the window function.

Thanks in advance