Dolby atmos only working in some videos

[alme55]

Hello, this is my first time posting here, hopefully it is in the right place.

I am having some issues with getting Dolby Atmos to work with Plex. I did quite a bit of trouble shooting and messing around to get it to work and couldn’t.
I am using a pc with windows 10, LG C7 oled tv and a LG SK10Y soundbar.

Initially i ripped my bluray copies of John Wick 2 and Avengers Infinity War to a .mkv format and tried playing them on both my pc’s plex player and my Lg tv’s plex player and atmos was not working through the plex app on either device. I tried playing both videos with VLC for windows 10 and sure enough they worked with atmos just fine. I also tried downloading a 4k atmos version of both movies as well, just in case i might have done something wrong and i got the same result, works in vlc but not in either plex players.
The next thing i tried was to get some videos that weren’t ripped form a disk that has atmos and try that, i got “The Haunting Of Hill House” and “Hold the Dark” (I do have netflix, this was just to test). To my surprise they both worked with atmos enabled and working through the plex apps on my tv and on windows 10. I tried a few more netflix movies and they all worked as well.

Has anyone else encountered this? and does anyone know what i might be able to do to get my bluray movies with atmos working in the plex app?

The best info i could find was that streaming sites like netflix use “Dolby Digital Plus + Atmos” and bluray disks use “TrueHD + Atmos”. Is it something where TrueHD + Atmos doesn’t work with plex? because i do see the option to select TrueHD 7.1 and AC3 5.1 when i play the movies, but atmos still won’t work when i do.

[FordGuy61]

@alme55

The best info i could find was that streaming sites like netflix use “Dolby Digital Plus + Atmos” and bluray disks use “TrueHD + Atmos”. Is it something where TrueHD + Atmos doesn’t work with plex? because i do see the option to select TrueHD 7.1 and AC3 5.1 when i play the movies, but atmos still won’t work when i do.

It is not a problem with Plex. It is a hardware limitation.

The TV cannot pass TrueHD audio to the soundbar. It is a limitation of HDMI-ARC and Toslink/Optical connections. Neither has the bandwidth to pass lossless audio - TrueHD, TrueHD + Atmos, dts-HD MA, dts:X.

So, when you play a video and select the TrueHD audio track, Plex will transcode the audio to a format that can pass to the soundbar (Dolby Digital, Dolby Digital Plus, AAC, etc).

As you found out, the streaming services use “Dolby Digital Plus + Atmos,” which can pass over HDMI-ARC. That is why you get Atmos audio when streaming from Netflix & other such services.

If you want to play TrueHD & TrueHD + Atmos audio w/o transcoding, you will have to use a streaming box/stick and attach it directly to the soundbar. AFAIK, the Nvidia Shield is the only off-the-shelf streaming box that will passthrough / bitstream TrueHD & TrueHD + Atmos audio.

You might be able to use Plex Media Player on a PC or Mac connected to the soundbar via HDMI and pass TrueHD + Atmos. Not sure if HDR works with this kind of setup. FYI, might = people in other threads have reported doing this, but I haven’t tried it myself.

FWIW, this issue goes away when products with HDMI 2.1 start shipping in 2019. HDMI 2.1 includes HDMI-eARC, which has the bandwidth to support lossless audio.

[alme55]

So basically, because the Plex app on the tv’s Operating System has to send the signal back to the soundbar over HDMI-ARC “which doesn’t have the bandwidth”, the audio gets converted down. Thanks for clarifying this, i had no idea.

But this doesn’t explain why my computer which is connected directly to the sound bar via HDMI will play TrueHD+Atmos audio in VLC player but not in either of the Plex desktop or Windows store players. If it were a bandwidth issue for HDMI then why is it working in VLC.

The only thing i can think of is maybe the Plex players for windows also does the same auto trans-coding conversion of the TrueHD audio that the tv’s Plex player does regardless of bandwidth limitations. Which begs the question would the Plex Player on the Shield also do this as well? Or can you disable audio trans-coding? i checked in the windows plex player and couldn’t find that option.

@FordGuy61

You might be able to use Plex Media Player on a PC or Mac connected to the soundbar via HDMI and pass TrueHD + Atmos. Not sure if HDR works with this kind of setup. FYI, might = people in other threads have reported doing this, but I haven’t tried it myself.

FWIW, this issue goes away when products with HDMI 2.1 start shipping in 2019. HDMI 2.1 includes HDMI-eARC, which has the bandwidth to support lossless audio.

As a side note, my pc is connected to the sound bar via hdmi in, then the sound bar is connected to the tv via hdmi-arc out. I am able to achieve 4k HDR 12bit 4:4:4 @ 30hz, i do encounter artifacting sometimes when i play games, and to get it to work i had to buy 2 cables that were rated at hdmi 2.1 to be able to get it going. When i tried hdmi 2.0 cables it wouldn’t work, took me quite a while to figure that out.
4k @ 60hz will work but i have to disable HDR.
As you eluded to before though, i am sure it is just an hdmi 2.0 limitation for now. The only thing i think the hdmi 2.1 cables help with is they allow the hdmi 2.0 ports on the devices to send the maximum bandwidth possible for hdmi 2.0.

[FordGuy61]

@alme55

But this doesn’t explain why my computer which is connected directly to the sound bar via HDMI will play TrueHD+Atmos audio in VLC player but not in either of the Plex desktop or Windows store players. If it were a bandwidth issue for HDMI then why is it working in VLC.

Re: Audio Bandwidth

The limitation is only from the TV to the soundbar, not from devices (PCs, set top boxes, etc) to the soundbar.

Audio passing from the TV to the soundbar uses the Audio Return Channel (ARC) part of HDMI. ARC was added to the original HDMI specification so you don’t have to run an optical cable to get TV audio to your soundbar, receiver, etc. Unfortunately, it has the same bandwidth limits as optical, so no multi-channel lossless audio such as TrueHD & dts-HD MA.

Audio that travels with video, from blu-ray players, streaming boxes, etc, does not have this bandwidth limitation. That is why such devices can feed lossless audio to the soundbar.

Re: Plex Windows Store App

Dump it. It hasn’t been updated since May 2017.

Re: Plex Media Player on PC

Plex is really good at hiding the settings in this app. The ones to look at are when PMP is in the “TV Layout.”

Launch PMP. Look in upper right. You’ll see the letters “TV” in a rectangular box, next to the Full Screen arrows. Click on it. This puts the player into the TV Layout.

Note: I have to use the arrow keys on my keyboard to navigate some of the menus at this point.

To get into settings, select your User picture/letter, then choose Settings.

Choose Audio → Device Type. Change from Basic to HDMI. You should now see several settings to passthrough various audio codecs. TrueHD is at the bottom. Select it if unchecked.

This might let you pass TrueHD + Atmos from your PC to the soundbar.

See pics below

Re: 4K60p, 4:4:4, etc.

See Wikipedia entry for HDMI. Specifically, the “Refresh frequency limits for standard video” and “Refresh frequency limits for HDR10 video” tables.

Some things to note:

• 4Kp60 HDR is limited to 4:2:2 for HDMI 2.0.
• The LG C7 is a 10-bit panel (I’ve the B7 which is also 10-bit).
• HDR10 movies on Blu-ray have 4:2:0 chroma subsampling.

You might try setting the PC to 10-bit instead of 12. It will push less data down the HDMI cable which should improve stability (tearing, etc). The TV doesn’t use those extra 2 bits anyway.

Also try setting the chroma subsampling to 4:2:2 or 4:2:0. This brings things back within the limits of HDMI 2.0.

---

Plex Media Player Settings

Select TV to change to TV Layout

To get to settings in TV Layout

Change Audio Device Type to HDMI and Passthrough options become available

[alme55]

I made the changes in PMP and it is all working now,
thank you so much for your advice and help. I really would not have been able to solve this without it.

@FordGuy61

Some things to note:

• 4Kp60 HDR is limited to 4:2:2 for HDMI 2.0.
• The LG C7 is a 10-bit panel (I’ve the B7 which is also 10-bit).
• HDR10 movies on Blu-ray have 4:2:0 chroma subsampling.

You might try setting the PC to 10-bit instead of 12. It will push less data down the HDMI cable which should improve stability (tearing, etc). The TV doesn’t use those extra 2 bits anyway.

Also try setting the chroma subsampling to 4:2:2 or 4:2:0. This brings things back within the limits of HDMI 2.0.

I also go this to work as well and now the TV is displaying at 4k@60hz, HDR 4:2:2, 10bit.
After enabling HDR in the windows display settings, I had to change it in the nvidia control panel:

Steps for how to change the settings if anyone else needs it
go to the change resolution tab on the left

change output color format to YCbCr422 - the hit Apply

The 10bpc option will apear in the dropdown menu after enabling YCbCr422, select it and Apply

Then change refresh rate to 60

[FordGuy61]

Glad things are working.

Thanks for detail on Nvidia control panel.

Cheers.