If you are watching a video, and notice that the actors don’t have lip sync, please keep the video or stream in XBMC open and playing, and click the little round speaker icon towards the bottom of the screen.
Different skins may use different icons, but one of the playback GUI buttons will take you to the window you need.
In the window that appears, click on the Audio offset entry, and adjust the slider until lip sync is achieved.
If all videos do not achieve lip sync, then return to the previous menu and then click the Set as default for all videos entry, this setting will then be saved for all streams.