Can you tell at which moments exactly you get artifacts? I assume it's always the same place. And what players did you use, what's your computer configuration? Why I'm asking because I have the same problems with other my own-made long videos, and don't know why. If you can, try 1.5 gb file. If everything goes right I will probably re-convert the fullhd-video with different parameters.
Sorry for late reply, was out of town for the weekend
I always get a bit of lag at the start, when it changes from the DxM logo and the video starts. Other than that its just more or less random trough the video. This was with VLC. Currently running a Pentium dual-core 3Ghz, 6GB ram, GeForce GT320 (I know, this is a pretty low-end card, but you'd be surprised at its performance).
I suspect my problem might be the graphics card, but then again it has never offered me any problems at all, neither at gaming nor watching HD videos, its only this format that keeps annoying me :|