Every time I encoded a video I’ve been working on from the enormous .avi format to .mp4, it was washing out all my colours. My very light background texture was all but disappearing, and everything looked like rubbish.
After lots of investigation, it was the settings in VLC which were doing it. I turned my brightness correction down in VLC and from then was able to encode the video to web formats without that extra brightness.
You may also find the same sort of ‘global’ video settings in your graphics card software – CCC or whatever nvidea’s one is.