If the problem is only with 4K content your problem is very likley due to the fact that 4K images (2160 versus 1080) are 4 times the data and consequently can be 4 times the video delay which will allow the audio to arrive well ahead of the image unless compensated for by an equivalent audio delay.
Since there is currently no synchronication data to define when audio and video were ever in sync (that may change in the future) broadcasters are "supposed to" insert audio delays to match video delays every time they do anything that can delay the video (any digital video effect - DVE - will delay the video). Unfortunately that is an open loop control system (measure video delay and add equal video delay) with no feedback so any mistake will result in a lip-sync error in the signal that cannot be detected downstream automatically.
The problem starts at content creation and there is very little a broadcaster can do to correct signals that already have lip-sync error when they receive them.
Add to this problem the fact that flat screen TV's also delay video ( many 80 to 100 ms) and lip-sync is a moving target often changing beteeen every program and sound almost always arrives before the accompalying image. If broadcasters over correct it is possible audio may arrive delayed but that's rare.
Most people don't consciously notice lip-sync error below about 50 ms and some are even more tolerant and can ignore 100 ms but a study at Stanford over 20 years ago showed even viewers who didn't consciously notice the problem suffered the same negative impact on their perception. The feelings about the characters they statistically correlated are the same as we have about people who don't make eye contact with us.
All viewers felt the characters were "more agitated, less truthful, less persuasive, etc.so it seems we subconsciously look away from the lip movement to avoid being confronted with the impossible - sound "before' the action that creates the sound - but are left with the same impression as if the charaters were the ones not making eye contact with us.
Google "Reeves and Voelker Audio Asynchrony" if you are interested in that research.
This also explains why in forums like this some viewers with identical equipment will report lip-sync problems while othres see no problem at all. Our "threshold of recognition" - the value of error at which we can no longer look far enough away to avoid noticing it - varies tremendously and will drop radically - sometimes to a few milli seconds - as soon as we finally notice it.
And then - when finally in our conscious- reducing the error to its former level often does not correct the problem. (You can't un-ring the bell.) That is to say you might ignore 80 ms error but aftre noticing 100 ms error you might be able to detect a few ms error.
It is an insidious problem that can only be truly corrected by adjusting the audio video alignment while watching.
I do this with a Felston digital audio delay but other companies like Alchemy2 and Primare (Primare Delay Box) make lip-sync correction products too.
If you set all other audio delays that may be offered by your equipment (TV's, AV receivers, and even DVD/BluRay players sometimes have delay settings) to zero and let an external delay provide all delay needed for correction your TV's inherent video delay will normally allow you to correct for arriving audio delay which does happen occassionally.
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