I am trying to watch a 1080p video on my Macbook Retina 13 but it is scaled up to the 'scaled resolution' 1280x800. If the video is scaled down to 1280x800 before being displayed, I will be losing in precision. VLC for example claims to support Retina Displays but that seems to only concern the fonts and not the video.
You can't watch any full screen video that is not in the exact native display resolution without scaling. At least in my knowledge.
The question is - is the scaling good or not. You may try different players.
If you want pixel to pixel mapping, you can only set the player size to 100% of the video, and it'll show as one of the windows on the screen, depending on the video file resolution - but only that way will you have the pixel-accurate playback.
Somebody correct me if I'm wrong.