If you speed up audio then you would have to speed up the video parts exactly same!
How would you keep audio and video in sync then, if not speeded up the same way?
Fundamental you can only speed up pre-produced content, not "live content"
as in OBS. Otherwise you could have a foresight into the future. =D
Regarding youtubes play-speed changes:
Youtube speeds up both of them (video too), naturally, not only the audio. They do it a special trick for the audio. They speed up and shift/pitch down sametime. So the sound keeps its pitch (mostly), to the price of small crackles, changed timbre and smallest parts left out.
So what do you want?
