Try this, delete the cache files in Application Data folder. May need to unhide the hidden folders in Windows.
Assuming you use Nvidia,
Go to advanced in the display control panel, find the settings for the card itself. Switch AA off, Anisotropic filtering off, Image quality set to high performance, Vsnyc off, Triple buffering off, Negative LOD bias allow.
INI changes - AllowScreenshots on, Bink16bit on, all other Bink related settings set to 0, SyncInput off, D3X9 queries off.
I did these changes and now my videos run smoothly even into late game. Although I do not know if it is down to changing one setting somewhere or a combination of settings or just by simply deleting the cache. The game is set to a different res than the normal windows res, but it seems to work happily here now.