I tried many things over the last few days on my Asus laptop, windows 10, 64bit, Nvidia Geforce 850M
What finally worked
Updating ATK (ATKACPI driver and hotkey-related utilities) from Asus site to latest Version V1.0.0041
I also updated smart gesture to latest version Version V4.0.9
From Support Center | ASUS USA - search for your model's driver updates page.
I just happened to do this because I noticed with win 10 I couldn't turn off my touchpad.
So I stumbled on this fix after many updates and rollbacks of GPU drivers, LR versions (6.0 wouldn't handle video for me either), and the video_toolkit.dll fix.
LR 6.3 is now importing and playing video as expected. I hope this helps someone else.