Hi can someone fill me in if the TV and or soundbar you use would trigger this issue? I was using a Samsung The Frame TV connect to my Apple TV 4K for about 2 years and never had any issues with Plex.
Recently I updated my TV to LG C2 and a Sonia Arc connected via eARC and now suddenly I’m experiencing audio sync issues.
So is this issue related to specific hardware you use or is my problem something else? Thanks!
You also probably updated your ATV in the meantime, right ?
But yes, issue seems to be hardware linked, and depending on your setup, you may or may not experience the issue.
For example, I have some, not for all files it seems, and I have a 2022 ATV directly connected to my LG 48C1.
Some fixes are tested via the beta channel as stated above.
LG CX and Sonos Arc for me.
I’ve previously seen the audio lip sync issue on two different theaters, each with an AppleTV 4K:
Upstairs: LG CX OLED directly connected via eARC to a Sonos Arc
Downstairs: JVC DLA-NX7 projector connected via HDMI to a Marantz AV8802 preamp (driving a bunch of JBL Synthesis speakers, but I don’t think that’s relevant)
I’ve opted into the beta (meaning using v8.14 with “flagged-off” enabled via @DaveBinM ) on both AppleTVs, set Plex to use new video player, and enabled matching both frame rate/format in Apple TV video settings. So far have not seen the sync issue, but also haven’t watched enough content yet to have a useful opinion. But so far so good!
When you say opted into the beta, you mean the 8.14 with “flagged-off” enabled? Frame rate matching is a little frustrating sometimes depending on how old the TV is when watching YouTube etc. depending on the age of the TV with black screen blinking 3-4 times every 5 minutes. (TV set to SDR 4K which seems to be still preferred with the Apple TV 4K and instead matching Range only)
Correct, I’m using the latest 8.14 beta with the beta chances enabled thanks to DaveBinM.
I haven’t had issues personally with the frame rate matching (I think), but do find the black blinking screen that pops up when Apple TV tries to match range annoying. Usually because it detects Dolby Vision. I’d be worried about using SDR 4K setting since I assume you lose the benefit of HDR and/or DV?
I think, and I may be wrong here, but still today in 2023 the suggested setting on “all” Apple TV 4K versions is still to set the video to SDR 4K, and tick the “Match Dynamic Range” flag in settings to allow for the conversion to HDR.
I’d love to hear from others if this is the case (ie, the current recommendation)? I’m slightly concerned by your use of the word “conversion” - is there some sort of conversion happening, or does matching dynamic range mean if HDR or DV is detected it will simply pass it through? And I guess a follow up question is whether there is a disadvantage to setting the AppleTV 4K to SDR 4K and matching dynamic range? What am I missing? 
A lot of tech YouTubers, setup guides, AV enthusiasts etc. suggest having match content on (frame rate and/or range). I would consider having those settings off to be a conversion of some sort.
What you’re saying is correct, having match dynamic range on passes through HDR or DV if the app allows it without changing it to something else. There shouldn’t be any disadvantages, unless you prefer having the AppleTV map everything to DV, which I believe is still the default setting.
The only disadvantage should be with the frame rate setting, that causes the screen to go black for a second and in some apps could have a sync issue. Then it’s up to you if you feel that having the AppleTV passthrough the native frame rate of the content is worth it (for me it is).
I have mine setup the same way — 4K SDR with match content on (but both settings for me)
Lg C1 with sonos ARC.
After upgrading to the 8.14 beta with “flagged-off” enabled no more lip sync. Thank you @DaveBinM
We probably shouldn’t do this in this forum string since this is not related to Plex audio synk issues on Apple TV 4K and stay on-topic, but you can google it and formulate what is the best option. I honestly don’t know.
You can read this article or follow the massive disagreements on reddit or google. Apple TV 4K tips and tricks | Digital Trends
Snippet for you:
" By default, your Apple TV 4K is going to communicate with your TV and determine what the best video settings will be. It may ask you if you want to turn on HDR, and you can go ahead and say “yes” if you have an HDR TV. If you do that, though, your Apple TV will always be in some kind of HDR mode, be that Dolby Vision, HDR 10+, or HDR, depending on your TV. This means that if you watch content that wasn’t made in HDR, you’ll be getting fake HDR, and you may not want that. Especially with really dark content — ahem, Game of Thrones.
There are two options I encourage you to explore. Choose Settings > Video and audio > Match content. Here, you can select Match dynamic range, which means that the Apple TV will go to SDR mode when you’re watching content made in SDR and then help your TV kick into HDR mode when watching HDR content. It’s the same idea with Match Frame Rate. Rather than show all content at the same frame rate, you can have the Apple TV deliver the content as it was made — this is especially important if you like watching movies in 24 frames per second, as they were made — otherwise, they can look artificially smoothed out."
So updated the Plex server on my Synology server, and using the latest version of the app on my Apple TV (8.13) with the new video player enabled. I’m using the Apple TV in 4K SDR with Match Dynamic Range and Match Framerate turned on and Audio output set to “Auto, Atmos Available”. Tried again but audio sync is still messed up. How do I enable the beta flag to try the potential fixes?
First of all you need the 8.14 beta version, to get that you need to enroll in the Beta program which requires Plex Pass. Then, to enable the actual audio fixes you need to DM @DaveBinM with your username so he can enable the fixes specifically for you.
The TestFlight betas do not require Plex Pass.
OK @DaveBinM then how do I enroll for the test flight betas?
Have a look here: Join App Betas: Android (mobile), Android TV, Apple TV, iOS
@DaveBinM It says “This beta is full” on the Apple TestFlight page so I can’t join 
Keep trying. I just installed it no problem.
@DaveBinM any chance you can clear some of the old non-using test flight users? trying to join the TestFlight but just says full?
We can try and clear some more, but we cleared 300 places just earlier this week, and it seems they’ve filled up again.
