On some computers running Windows 8, when you play specific video files in Windows Media Player, or in the Xbox Video app, you may notice some visible distortion (video artifacts) during the first few moments of playback. For example, there may be colored macroblocking artifacts in the bottom portion of the video frame.
After a few seconds, the distortion goes away, and the video plays normally.
Microsoft has confirmed that this is a bug in the Microsoft products that are listed in the "Applies to" section.
This problem occurs because of a bug in the Windows video decoder when it starts playback and decodes the first video frame. It is most likely to occur when playing videos which are encoded using a very high bitrate. Due to implementation differences between different graphics drivers, the problem may not occur on all computers.
To work around this issue, leave the video clip open in the application and restart playback of the video. On subsequent plays, the distortion will not be visible.