Video AF is generally a waste of time.
I know its not for everybody but hyperfocal and zone focusing are a better idea, which requires a lens with markings and an awareness of the effect of focal length and aperture on depth of field.
Video af is lousy enough on 1/8th type consumer cameras, add in much larger sensors with the effect that has on Af and its a miracle some systems work as 'well' as they do.
Then the there is the issue of what to actually focus on, and to be able to track that when the subject and possibly the camera is moving.
In comparison, stills af only has to be in focus at moment you take the picture, a usable video af system would need to be fast intelligent adaptive and contiguous.
If you want video without having to focus then get a fixed lens canera like a flip, or a consumer cam with a tiny sensor.
If you want to shoot in focus video on a large sensor camera you need to do it yourself. And believe me, it isn't easy.