Audio lag when showing video in PPT on external screen with HDMI cable.

The other day I accidentally hit a combination of buttons that resulted in a pop up box briefly appearing with a message along the lines of 'delay audio by 5ms'. Since then all embedded videos in PPT have this audio lag issue. I have restarted PPT and my computer and the issue remains. I can not see any way to reverse this and I can not select 'undo'.