Why is full-screen casting unavailable for iPad?

ViewBoard has an aspect ratio of 16:9, but the iPad's aspect ratio is different. Therefore, when the iPad is displayed in proportion to the ViewBoard, black frames will appear on both sides.

Why do I get a black screen when using Vcast and Youtube/Amazon prime/Netflix?

Refer to this FAQ. 

How to use "Mirroring"?

1. Connect your phone to the same network as the ViewBoard. 2. Open the control center. 3. Click “AirPlay” and select the ViewBoard device name for wireless display.