To: pondycastle
The problem of upper-left image (partially displayed video) on preview is actual for scalable GUI and some video cards NVidia in Windows 8/8.1/10 with enlarged/increased DPI (scale 125%, 150%, 200%, etc.). The issue is related to video card drivers or its settings.
"Use video buffer" is a new option in our video-products from release 2017.01 and is intended for solving that problem. Previously, we used only one mode of video rendering - "Allow video overlay" (by default). Now we give you the possibility to change mode depending on the situation.
Using of video buffer allows you to solve problems of black screen or partially displayed video, to output video to the second screen and to make screenshots in the usual way (PrintScreen, Alt+PrintScreen).
If everything is OK, we recommend to users to use a video overlay, and in case of problems - a video buffer.
You can set this option here:
Settings -> Preview -> Video rendering.