Windows Media Player Is Out of Sync
When the audio is out of sync, even by a half-second, watching videos can quickly become an aggravating experience. If you're using Windows Media Player, you can fix this problem by having the player drop a few frames when needed in order to keep the audio in step with what's on the screen. In most cases you won't notice a drop in video quality.
Click the Windows Media Player "Organize" tab and select "Options" from the drop-down menu.
Click the “Performance” tab. Click the “Drop Frames to Keep Audio and Video Synchronized” check box to activate this option. Check the “Turn on DirectX Video Acceleration for WMV files" check box if it isn't already selected.
Click “Apply” and click “OK.” Restart Windows Media Player and open a video file. Ensure that the audio and video are in sync.