There are DJ and VJ Tools which pitches Audio and video without nearly any CPU usage.
All of this is done before anything is handed over to the output.
And they dont have pitch fluctuations and other kodi styled problems.
Also kodi dont need "sync playback to display" it just needs a pitch stable PAL speedup.
Get your fav tv show and then pitch it down by 4,xx% then u know how sleepy, boring it sounds watching a 24p tv show with german synchro, where the synchro was done for 25p.
e.g. Lost