Maybe it would help if you understood what causes audio to not be in sync with the video and what HDMI lip sync is supposed to be doing? I say suppose because it requires the way it is implimented onboard all the devices in the HDMI chain to be compatable with one another.
There's been a lip sync feature of HDMI since the advent of version 1.3, allowing audio processing to be automatically adjusted to compensate for errors in audio/video timing.
There isn't apparently any HDMI-ATC system level Lip Sync performance
compliance specifications, or test tools designed to ensure accurate Lip Sync delivery. There is no “timing conformance” specification that must be demonstrated to any authority in order to build a compliant product. This has led to no real way of confirming whether one manufacturers claims regarding lip sync are in accordance with what would actually pass as auto lip sync or whether the way one manufacturer has implimented it corresponds with how another has.
Audio-video synchronization errors are occurring more frequently. This is mainly due to increased digital processing being implemented into devices. Getting the manufacturers to actually own up to this is also not helping and many deny there is a problem, believing the audio/video asynchronies in their devices to be imperceptible and or acceptable.
The ever increasing amount of video processing being employed and implemented into devices has given rise to more instance of lip sync issues. Audio and video synchronisation problems occur because
video processing is more intensive than audio processing. Because of this, the audio is ready for playback before the video, and if audio is not delayed, what viewers hear will not match what they see on the screen.
It is true that not everyone reacts or perceives such anomalies in the same way. The extent to which a consumer can tolerate asynchronies is dependent upon human perceptual limits as well as personal taste. After saying this, studies have been done and conclusions have been made as to what is and what isn'r acceptable.
As far back as 1998, ITU-R published BT.1359, recommending the relative timing of sound and vision for broadcasting. Studies by the ITU and others have suggested that thresholds of timing for viewer detection are about +45ms to -125ms, and the thresholds of acceptability are about +90ms to -185ms. In addition, the ATSC Implementation Subcommittee IS-191 has found that under all operational situations, the sound program should never lead the video program by more than 15ms and should never lag the video program by more than 45ms ±15ms.
Also be aware that anywhere video is processed, there will be a delay.This is unavoidable whether you can perceive it or not. The issue is how should the manufacturers compensate for this before it does become perceivable? Faster processing helps, but will still result in video delay, plus the fact that more and more of the video features consumers now expect are very heavilly dependant upon video processing. More features means more processing and the increased chance of audio being out of sync with the video.
The adjustment as implimented with HDMI 1.3 were based on a previously estimated delay factor.
The method of automatically delaying the audio by an estimated factor, based on the expected delay in the video signal during processing as introduced with HDMI version 1.3 is imperfect. The correction is basically guessing as to what the delay is or will be.
HDMI 2.0 introduced dynamic auto lip-sync. This supposedly synchronises the audio and the video dynamically irrespective of the various HDMI sources. The facts of the matter are that people still experience lip sync issues despite having HDMI version 2.0 equipped devices and auto lip sync engaged.