I downloaded the file and VLC says it's supposed to be a 720x486 file, but when I size it to 100% there are about 20 pixel black bars on each side of the frame. So it appears the video is squished and black bars are added to the sides to make it 720x486.
In Quicktime, there's what looks like a 40-50pixel white bar on the right side, and again, it appears the video is squished and the white bar is somehow getting added to make the file 720x486. Quicktime reports the format as H.264 at 654x486, but it reports the normal size as 720x486...which is very strange.
Your movie also displayed this way (with the white bar) in mutliple browsers when I played it. So it looks like something is messed up with your sizing on the file, which could account for the artifacting. We'd need to know what you used to compress it, what the original file is (format/codec), what settings you're using in the compression program etc.
It's probably best to size for computer screens if that's your final output & playback...so if it's a 4:3 file, something like 640x480 is going to work better on a computer screen.