I have this problem with some movie files I download, doesn't matter if they are big or small, or downloaded through the web or emule, and I haven't been able to isolate the cause of it. What happens is the first frame just flashes quickly over and over, while the timer shows the movie playing. Sound works, but the film just keeps on flashing. If I try to jump forward, nothing happens. And with some other movies, it plays for a few seconds, then starts the flashing on whatever frame it is at. Any ideas?
Use Gspot to determine which codecs you need. IF you get a fourCC code of '0' then its most likely the file is fake.
AviCodec is also a good program Oriphus, its rare u see a fake on emule because u get your files from web sites like sharereactor and they arent gonna post up fakes!