This is from the background construction buffer. It has terrain and buildings, but no fog or units. Why warvid would be capturing it is a bit of a mystery.
It's reasonable to think that it could be copied to the screen buffer before the fog and units are applied to it, but in this case i would expect warvid to be capturing it all the time. It's certianly not a video or display driver issue of any sort. If it's a win8/10 thing I can only think that maybe it could be due to a core change in the way windows impliments multi-tasking i.e. if it is interrupting the WC2 process part way through rendering a screen frame.
Of course it would be relatively simple to make a hack that copied this to the screen output buffer a few times a second, perhaps when a hotkey is pressed, which would give a player a filckering look through the fog - certianly enough to see where people have halled...
The most unbelievable part of that scenario is why on earth lone would have posted this warvid if that were the case. Weird