If it only freezes in that one app, then the problem isn't the tablet, it is the app or your connection. I would look into the app being the issue first. If these are downloaded videos, then try clearing out the apps cache and see if that will make it run faster. Or if not, then try uninstalling the app, restart the tablet (turn it off and back on) and then reinstall the app.
Now if the videos you are viewing are online, rather than on the device, then you should also check your internet connection to see of the speed drops. That could cause this problem as well.