I was aware that you're from The Netherlands and consequently that - most probably - Dutch was your native language. That's why I mentioned that particular site (as well as "Brein").
Very strange phenomenon indeed. You did not mention what type of file (and codec used) your movie-file is. [Check item 2 of my Help-to-Help post; link hereunder].
Is it perhaps possible to load it in (e.g.) VirtualDub (and make a "direct stream" copy
(setting for both audio and video))?