I've been doing some reading on the Mavic as I am interested in the mavic. I was wondering if the video from the Mavic Pro was transported over wifi back to the smart device or does the video get to the smart device via the USB cable?

Thank you

It got to be a the cable that is transferring that data from the RC to the phone, it is awful lot of information such as 1080p video, flight data, commands from phone to RC, etc.

It is absolutely the cable that connects your phone to the controller. The Mavic sends the video feed to the controller via occusync (because wifi and bluetooth are very short range), which then sends it via usb to the phone/tablet. How do I know? Because the app and video still work when your phone is in airplane mode (all wireless functions off), and I am 99% certain that the video does not go from the controller via osmosis.

Now, if you are flying in WiFi mode, without the controller, then control of the Mavic AND video are both transmitted over WiFi, to the limit of the WiFi range, or about 800ft (250 metres?)

If you use the USB A port under the phone mounts for a tablet instead of the dji proprietary micro-usb cable for phone, then make sure it's a good one, that supports USB 3.