I've got a problem with AVC video decoding. Whenever I play an AVCHD format video (and possibly others as well but I'm not sure,) artifacts like this appear for a few frames every now and then (it ranges from once in 10 minutes to every 30 seconds):

The artifacts are not encoded in the video as when I go back and play the same shot again it plays flawlessly.

I have KLM Mega codec pack installed and use Media Player Classic for playback (but the artifacts appear in VLC and WMP as well).

I tried installing a new version of just about everything and it still does this.