I read the whole thread:
http://www.flickr.com/groups/canoneos5dmarkii/discuss/72157624908100888/
and tried Video LAN VLC Player and set "Skip the loop filter for H.264 decoding" to ALL. It made no difference. Videos taken by a newer Casio camera have no problem. The computer is very powerful. Thanks for any advice.
When using a computer to play the video taken on this Canon PowerShot A520, the screen flickers a little bit, dark - bright - dark -..., about once a second or faster. Is there an easy way to fix it?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic