I have an LG OLED55C9 hooked up to a Denon AVR-S750H receiver. Both support eARC.
When using other apps on the TV (like Disney+), I am able to get high-definition sound (e.g. Dolby Atmos). However, with the Plex app I cannot.
The only options showing in Sound settings are AC3, EAC3, & DTS.
Does the Plex app on LG TVs not yet support high definition sound?
If not, is there another local media streaming LG TV app that does (e.g. XPlayer)?
There are two types of Atmos for home theater, “Streaming Atmos” and “Blu-ray Atmos.”
“Streaming Atmos” is EAC3 + Atmos and is used by the streaming services, Disney, Netflix, Amazon, etc. Given that EAC3/Dolby Digital Plus is lossy, it is not generally considered high-definition audio.
“Blu-ray Atmos” is TrueHD 7.1 + Atmos and is what is on Blu-ray discs. TrueHD is a lossless codec, and is considered high-definition audio by most people.
Unfortunately, HDMI-eARC does not seem to pass lossless audio (TrueHD, TrueHD+ Atmos, dts-HD MA, dts:X) from TV apps (any app, not just Plex). It only passes lossless audio from devices attached to the TV via HDMI.
This is a limitation of the TV, not Plex. It seems to be a limitation of all TVs, not just LG.
If you want “TrueHD + Atmos” audio, your only choice is to use a Nvidia Shield. It is the only off the shelf device that will passthrough TrueHD audio (Plex Media Player will passthrough TrueHD, but does not support HDR video).
If you do purchase a Nvidia Shield, buy the 2019 Pro. The non-Pro, aka “Tube”, has limited RAM and only supports 32-bit apps. There are multiple threads with people reporting problems with Plex on the non-Pro 2019 Shield.
Well, my issue is not a limitation of eARC, as
a) high-definition audio is key capability of eARC.
b) I mentioned that I’m already getting (lossy) high-definition audio (“streaming Atmos”) via eARC.
The question here is why I’m not getting any high-definition audio including DTS-MA via Plex. If Disney+ can do it, Plex should be able to do it.
A portion of the Netflix, Disney+ … etc fees goes towards paying for codec licenses which is what Plex would have to do to provide the same capability.
You are not getting high-definition audio via Disney+.
Disney uses “Streaming Atmos,” which is Dolby Digital Plus with Atmos metadata. This format also used by other streaming services such as Netflix, Amazon, Apple, etc. It is not usually considered high-definition because Dolby Digital Plus is a lossy audio format.
The Plex app already supports “Streaming Atmos.” Download demo files from Dolby and test with your system.
“Streaming Atmos” does not require HDMI-eARC. It can pass over HDMI-ARC. I’ve a LG B7 OLED and a Denon AVR-X4300, neither of which supports eARC. The Denon displays “Dolby Atmos” when I play the Dolby demo files. The Netflix and Amazon apps on my B7 also send Streaming Atmos audio to my receiver.
HDMI-eARC provides support for multi-channel lossless audio such as Dolby TrueHD, TrueHD + Atmo, dts-HD MA, and dts:X. The bandwidth required for these audio formats exceed the capacity of HDMI-ARC.
No TV app, Plex or other, will passthrough TrueHD, dts-HD MA, etc lossless audio via HDMI-eARC on any TV, LG or others. This limitation is seemingly imposed by the TV manufacturers or by the HDMI-eARC standard (it is unclear who is limiting things).
Thanks @pl_5309
So, you are saying Plex could technically implement - just has not yet?
No, I was merely pointing out that Plex has no way to cover the costs. You also have to consider the technical limitations of the devices themselves and probably the best that could be achieved would be Atmos Lite just like Disney.,
This is some good stuff, @FordGuy61 I think I see where you’re going here.
Some questions/comments…
You are not getting high-definition audio via Disney+.
Them’s fightin’ words. 
Some say high-def is lossless; some say it’s anything over “cd quality”. Regardless, it’s not streaming audio I am trying to get clarity on.
The Plex app already supports “Streaming Atmos.” Download demo files from Dolby and test with your system.
Thanks for this. Dolby Atmos is working on my rig just as you would expect.
Interestingly, Plex shows “Uknown” as the audio format, while it does show “DTS-MA” when playing a DTS-MA video.
“Streaming Atmos” does not require HDMI-eARC. It can pass over HDMI-ARC. I’ve a LG B7 OLED and a Denon AVR-X4300, neither of which supports eARC. The Denon displays “Dolby Atmos” when I play the Dolby demo files. The Netflix and Amazon apps on my B7 also send Streaming Atmos audio to my receiver.
I find this particularly interesting.
I had an LG OLED B6 hooked up via ARC to an Onkyo TX-NR555 and Dolby Atmos would not work. In the research I did, this was expected as DD+ was inconsistently implemented over ARC. I find it interesting that the 2016 model did not work, but the 2017 did. (or maybe your Denon receiver was the difference)
No TV app, Plex or other, will passthrough TrueHD, dts-HD MA, etc lossless audio via HDMI-eARC on any TV, LG or others. This limitation is seemingly imposed by the TV manufacturers or by the HDMI-eARC standard (it is unclear who is limiting things).
Kind of defeats a key purpose of eARC then. If you were able to get Dolby Atmos without eARC, then what’s the point? To simply get DD+ without having to turn on CEC?
Are you saying the Plex developers have confirmed it’s the TV or receiver that’s the issue - i.e. there is nothing in Plex code that needs to change?
I’d have to imagine that with eARC being relatively new, the TV app developers just haven’t spent much time providing support for lossless audio.
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