Not quite sure where to put this thread on, but under Apps>Multimedia seems to be exact.
I've noticed this problem for sometime now, that playing full HD videos (1920x1080 resolution ) on my 1600x900 monitor generates grainy graphics, by any chance a video player or plugin is available to tune them to my res, or soften the video?
I wouldn't want to convert the video since it would take loads of time considering i have more than 50 full HD videos.
More aboutrunning 1080p videos full monitors
Try another video player to see if it scales softer.