When I upload a video onto youtube, the result is a somewhat darker image than if I view the video via any other means (VLC player, windows media player, etc).

For instance in this video: http://www.youtube.com/watch?v=MTBI6IJKtnc at the 1:53 mark the dark background should have little white static hairs on it (using the hair FX from Sony Vegas), which appear fine when played locally, but after the youtube upload it's so dark that they're practically invisible. That's not to mention dark scenes in videos that of course look much, much worse than normal.

I am outputting the file as an mp4 with Sony Vegas, and even after outputting it it looks fine on my computer, just not after the youtube upload.

I have tried viewing on different computers also, and it's always the same.