You have not mentioned what Operating System you use. Based on your problem I suspect it's Windows 8 (but there are problematic Windows 7 configs as well). Your problem must be the hard to override buggy default Windows mpeg4 decoder. You should read the explanation and try Codec Tweak Tool. You can check the used filters by clicking "Active Filters" context menu item of Desktop Movie. If you don't see Ffdshow Video Decoder (but you see any MS decoder) then this is the solution for your problem.