Server Version#: 1.25.5.5492-6000
Player Version#: 5.31.1
I have a lifetime plex pass and DS920+ NAS with PMS installed.
I have a LG OLED BX smart TV with Plex app installed.
I have a Samsung HW-Q900A soundbar connected to the TV by HMDI 2.1.
While watching a dolby atmos movie on my TV from my plex library, i noticed it was being transcoded:
Does it mean that the sound lost every Atmos effect?
Is it an hardware limitation?
Thanks in advance !
It is a TV limitation. No TV supports playback of TrueHD audio via a TV based app.
If you play a TrueHD audio track using a Plex SmartTV app it will be transcoded by Plex Media Server. Any Atmos information is lost in the process.
The Plex app will passthrough Dolby Digital Plus + Atmos (EAC3 Atmos) to your soundbar. That format is used by the streaming services (Apple, Netflix, etc) and is supported by the TV.
If you want 4K HDR video and TrueHD + Atmos, you should acquire a Nvidia Shield Pro or Xbox One and attach it to an HMDI Input on the Samsung soundbar. The LG TV blocks passthrough of dts audio, so attaching the Shield/Xbox to the TV will result in Plex transcoding dts audio.
Also, do not purchase the Shield “tube” model. It has problems with high bit rate media, such as 4K HDR movie rips. If you buy a Shield, get the Pro model.
See this thread for additional details:
Thank you so much for replying this fast and clear. 
I understand that there are 2 formats able to carry Atmos metadata:
No TV app supports TrueHD format, which means that all the Atmos demo videos I watched on Youtube app were not working (losing Atmos metadata) ?
How big is the difference between TrueHD and EAC3? Does it worth buying the shield pro?
The answer depends on the quality of your sound system, your hearing, and your desire for Atmos audio.
First the Atmos part.
If you want Atmos audio when listening to Blu-ray rips, whether HD or 4K, you will need a Shield or Xbox. The Atmos audio tracks on Blu-ray discs are TrueHD + Atmos. When Plex transcodes TrueHD audio the Atmos information is lost in the process, even if the audio is transcoded to EAC3.
As mentioned earlier, EAC3 + Atmos is not a problem. The Plex SmartTV app can pass it over HDMI-ARC/eARC to the audio equipment.
TrueHD vs EAC3:
This is part objective and part subjective.
TrueHD definitely has the capacity for better sound, as it is lossless and handles higher bit rates and sample rates than lossy EAC3.
The source material also comes into play. For a 1960s Elvis Presley movie it most likely won’t matter which audio codec is used. The recording equipment at the time is the limiting factor. For a modern movie recorded digitally, and with the right sound system, it is possible to hear a difference between TrueHD and EAC3.
The sound system also matters. If you’re using TV speakers you won’t be able to tell a difference. With a nice soundbar or receiver you might.
Testing:
Here’s a way to test before deciding to buy a Shield/Xbox.
The Digital Theater has several trailers with TrueHD + Atmos and EAC3 + Atmos audio.
https://thedigitaltheater.com/dolby-trailers/
Download Chameleon or one of the other videos with both audio types and put it in an Other Videos library on your server.
Play it with the Plex app on your TV. See if you can hear a difference between TrueHD (which will transcode) and the EAC3 + Atmos audio track (which should direct play).
Second, if possible, connect a PC (not a Mac) to the HDMI input on the Samsung soundbar. Install Plex for Windows and configure it to passthru audio, including EAC3 & TrueHD. Play the same test video. Both the TrueHD and EAC3 audio tracks should direct play. That will let you hear how TrueHD + Atmos compares to EAC3 + Atmos. FYI, pretty certain Macs block TrueHD passthrough, which is why you can’t use one for this test.
That will give you a reference you can use when deciding whether or not to acquire a Shield or Xbox.
Plex for Windows Audio Passthrough
Connect PC to HDMI input on soundbar (soundbar must be turned on to choose correct settings).
Launch Plex for Windows.
Settings → Player. Click Show Advanced.
Audio Device: Default is Auto. Select a specific audio device (i.e. the soundbar).
Audio Device Kind: Choose HDMI.
Audio Channels and passthrough options will appear.
Choose number of audio channels. Should be OK to leave at Auto if desired.
Select desired audio formats to passthrough to soundbar.
Save changes.
Thanks again for your detailed reply ! And sorry for answering so late: I was in holliday 
.
I uploaded a few trailers from thedigitaltheater to my server, then tried to play them on my TV and the result is the same for all of them (chameleon, core universe, escape, leviathan and pufferfish).
Plex display 4 audio tracks as shown below:
If I select TRUEHD 7.1, Plex transcode as expected:
If I select EAC3 7.1, Plex direct play as expected:
Sadly, with this track selected, the only thing I can hear is an audio message saying “You are listening to the Dolby Digital companion track not the Dolby Atmos track this disc is intended to demonstrate.
To listen to the Dolby Atmos soundtrack please set your Blueray Player to bitstream out and connect your player to your Dolby Atmos enabled receiver via HDMI.”
Any idea why this is occuring?
Thanks !
UP, your help would still be appreciated
I can’t wait to hear from you 
There are 2 different audio tracks with different audio in them. Some devices cant handle atmos/trueHD so instead of just listening to nothing there is another audio track that says … hey … this is an atmos demo … please go listen to the atmos audio track… then it tries to help you do it… from your blueray player … because it is supposed to be … or was ripped off a disk. Its the same type thing when you are watching a movie with the movie audio or you are listening to the commentary. They have different stuff in them.
For most movies the audio content is the same with more of fewer channels/different encoding.
So if you are using plex on your TV ie … the tv is accepting the signal … and you arent sending the audio from the TV to something else … like a receiver then atmos/true HD isnt going to do anything for you. Having say 13/7 channels of audio coming out of 2 speakers … or … say 13 channels of audio being decoded/transcoded to 2 physical speakers …
Here is a valid use case.
You have a home audio receiver that is connected to your TV. You have other audio sources plugged into your receiver like an xbox etc. but your TV is the thing actually running plex.
So normally your TV would be the thing with the speakers outputting the audio. But hey you have a receiver with more speakers etc. It will pass the audio from the TV back down the HDMI cable to your receiver and play that audio (if the hardware supports it etc.) ARC audio return channel. It can only handle so many channels … eARC can do more … i cant remember how many it has been awhile.
So unless you have audio being passed back to something with more speakers … its not worth transcoding high definition audio meant for many speakers to your TV. It would be preferable for your plex to send the raw audio data to the TV for it to process it. Transcode means plex is processing it into something else before it hits your TV. (Usually because of the bitrate or your hardware cant natively decode the raw data stream.)
I currently have a 13.2 channel receiver with all the speakers except for 1 pair. Stuff sounds super cool when it works. I use appletvs most of the time but the plex app has gotten bloated and only runs well after doing a reboot of the ATV. I never used to have to do that. From only when the appletv did an update did i reboot. Every 3 to 12 months … to doing it weekly if not more often.
Cheers,
Hope this helps.
Thanks for your reply !
I’m not sure that you understood my situation.
My setup is: TV running Plex > HDMI eARC > soundbar compatible with Atmos.
FordGuy61 told me that no TV can passtrough Atmos, which explains why TrueHD Atmos audio tracks are transcoded, losing every atmos data by the way.
The only solutions then are:
To choose between these options, FordGuy61 told me to test some demo files available on “thedigitaltheater” website which contains both TrueHD and EAC3 audio tracks.
Next problem is: EAC3 audio tracks only say “You are listening to the Dolby Digital companion track not the Dolby Atmos track this disc is intended to demonstrate.
To listen to the Dolby Atmos soundtrack please set your Blueray Player to bitstream out and connect your player to your Dolby Atmos enabled receiver via HDMI.”
At this point, my question is: how can I really listen to EAC3 Atmos track in order to decide if it is good enough for me?
Thanks in advance !
Apologies for the belated reply. I lost track of the thread.
There is something strange happening with the LG app and picking the desired audio track.
With Chameleon and Core Universe if I pick the EAC3 + Atmos track I also hear the “wrong track” message.
If I pick the fourth / last audio track, I hear the EAC3 + Atmos audio and my receiver displays “Atmos.”
It seems limited to the Plex LG app. Plex Web, Plex for Windows, Plex for Android pick/play the audio tracks correctly.
No problem, you already helped a lot !
I tried to play each track of “Core Universe” on Plex TV app and here’s the result:
Maybe we can find pure EAC3 Atmos tracks?
That’s just weird. LOL.
Try Nature’s Fury. It has just one audio track: EAC3 5.1 + Atmos audio.
Edit: There are three Nature’s Fury videos listed. One is TrueHD 7.1 Atmos & EAC3 7.1 Atmos; one is EAC3 5.1 Atmos; one is TrueHD 7.1 Atmos.
You can disable EAC3 audio in the Plex app settings and the audio will transcode to AAC 5.1. That will let you compare how the audio sounds with and without Atmos. You could also play the Nature’s Fury with TrueHD. That should transcode to EAC3 audio, and Atmos will be lost during the transcode.
Outside of Plex, if you’ve a Netflix account you should be able to stream some videos with Atmos audio (look at the Netflix originals, many have Atmos). It is EAC3 5.1 + Atmos. Amazon has Atmos support in some of their movies too.
Each audio track can have its own content. They dont have to have the same stuff. If it was a rip of a disk. They may not have included the other tracks because it was meant to be an atmos demo. Grab some other media to test with that has the same content in each audio track. Then play with it.
I got this of the rtings site. (Excellent TV reviews.)
Our TV Input Tests: Audio Passthrough - RTINGS.com.
“To test for Dolby Atmos via TrueHD passthrough via eARC, we connect a PC to the TV via HDMI, and we connect a Sony STR-DH790 receiver in the ARC port. We make sure all the eARC settings are on, and we play an audio file in the Dolby Atmos format. If the receiver says ‘ATMOS’, it means the TV can pass Dolby Atmos signals. If it doesn’t support it, that means the audio format is limited to Dolby Digital, and you won’t get the same sound experience.”
Hope this helps,
Cheers.
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