I could only guess, but could it be because of a slow internet connection. Does it handle video that is not being downloaded the same way?
Perhaps it is your video driver, have you looked for an updated one?
Is you computer doing other things in the background that might be causing decompression errors?
I would mention something about codecs, but I do not know what would really be necessary for your system. If you do want to check which ones you have installed, type msinfo32 in the Start Menu search box and hit enter. Look under Components, then Multimedia.
While in the System Information window, check the problem devices also.