The video stuttering is from the original footage.
It's frame rate is claimed 25fps @4K
Examining raw video I've found it is duplicating frames but not consistent.
It is more like 22-23 fps with the dropped frames being replaced with a good frame eg duplicating a frame.
Something is out of sync.
I'm suprised this Dashcam has been on the market for a year.
It's a nice unit but the stuttering lets it down.
I'm sure it can be fixed via firmware (hope it can) Viofo fixed theirs.