Variable speed playback is very useful.
But in my practice, it will lead audio out of sync with picture.
It looks like the speed of picture and sound is a bit different; at first, they are sync, but gradually out of sync. The lag may be half second at last. If I pause and play again, the lag is reset to zero.
My device is atv4k, and the problem existed since variable speed function came out. But this did not happen in ipad/iphone infuse. I tried open “matches the frame rate of content" or not, it doesn’t work out.
Another notice is that when speed up, there is much stutter and judder, which is also not so much significant in ipad/iphone infuse.
I am having the same issue. iPad/iPhone has no sound issues but ATV 4K has issues after about 20 minutes using speed of 1.25x
Connected to my TCL 4K TV and using either homepod or soundbar