You could think that keeping sync between sound and picture must be easy those days, but TV channels, online streams, physical medias, TVs, projectors, players, computers, audio decoding gear, all have variations and the result is unpredictable. Best not to lose sleep over this, as this will never be perfect all the time!

If you can't determine a good setting, it's better to err on the side of the sound being a tad late than ahead. Our brain knows that sound may arrive late, like when the subject is at some distance. But it will be in great confusion when it's hearing something before it happened!