Not sure what the video playback issue is. Likely related to a problem with new hardware accelerated video encoding. Not sure what can be done to solve it, other than a soft reset or a hard reset is desperate enough. But even then, I really can't guarantee this will address it. Care to share where the video is from? What app you're using?
And yes, games hub sucks. Just with music, it's no longer a part of the OS, and is now store updateable. Seems ridiculous, as I'm not sure what major features they need to add overnight, and now it's entirely unoptimized and buggy. You can see it has a really low rating in the store. Thankfully, now that it's store updateable, they can quickly release a patch the moment it's available. So hopefully they get on that soon, because games hub (and music... and videos...) all SUCK right now. Happy with 8.1 overall, but these three hubs are the bane of my existence right now.