Video previews are here! I almost want to put this under a longer beta, but with some quick work arounds it is working pretty good. I did identify a crash caused by Nvidia GPU (i believe), which I am working on resolving. Works fine using Intel Integrated Graphics though. Users with only 1 GPU, will need to keep the preview disabled until I can determine the cause for the crash. I may just end up switching to another video renderer if nothing else pans out! Thanks for your patience!
Working video preview.
Open NVIDIA Control Panel.
Click Program Settings tab, then click "Add".
A list of recently accessed apps will show. If ThatFile doesn't show, click cancel, launch ThatFile, then re-click "Add", then locate ThatFile and select "Add Selected Program".
Select "Integrated Graphics" from pull-down menu, then click "Apply". ThatFile should now be ready to preview videos in Preview Window and Glance Window.