I downloaded the dolby atmos demo mp4 from dolby, and played it via my roku ultra, to my Anthem AVM60 receiver. I get dolby atmos, no problem. If I take a bluray that I converted (MakeMKV->plex), I get TrueHD, but no Dolby Atmos.
When playing the dolby atmos test file, in plex the audio shows up as Unknown (EAC3 5.1) - Direct Play. Receiver shows Dolby Atmos.
On the movie, I get English (TrueHD 7.1) EAC3 Transcode. Receiver shows Dolby D+ 3/4.
try converting the container from mkv to mp4 and test the movie. This can be accomplished pretty quickly using a quick conversion tool or even a batch script in ffmpeg
The problem is that a Roku does not passthrough TrueHD audio. This means that Plex must transcode the audio, and the Atmos data is lost in the process.
The only off the shelf device that will passthrough TrueHD + Atmos is a Nvidia Shield. The AppleTV 4K decodes TrueHD to PCM on the ATV4K itself (so Plex shows direct play). This preserves the lossless audio for TrueHD, but the Atmos data is still lost.
There are two versions of Atmos for home theater.
“Streaming Atmos” is EAC3 + Atmos and is what is used by Netflix, etc to deliver Atmos audio. It is also what is in the demo file you downloaded.
The Roku will passthrough EAC3, including EAC3 + Atmos, to your pre-amp. That is why you see “Dolby Atmos” on the pre-amp display when playing the demo file.
“Blu-ray Atmos” is TrueHD + Atmos and is what would be on the disc you ripped.
The Roku does not passthrough lossless audio such as TrueHD. Plex transcodes TrueHD to EAC3, so your pre-amp displays “Dolby D+.”
On the Roku website is says the device passes through Atmos, which it does, just not TrueHD + Atmos. Notice that TrueHD audio is not mentioned in the audio section.
Examine both files with MediaInfo and you can see the difference.
For the demo file you will see something similar to:
Format : E-AC-3 JOC
Format/Info : Enhanced AC-3 with Joint Object Coding
Commercial name : Dolby Digital Plus with Dolby Atmos
Codec ID : ec-3
Duration : 8 min 23 s
Bit rate mode : Constant
Bit rate : 448 kb/s
Channel(s) : 6 channels
Channel layout : L R C LFE Ls Rs
For the Blu-ray rip you will see something similar to:
Format : MLP FBA 16-ch
Format/Info : Meridian Lossless Packing FBA with 16-channel presentation
Commercial name : Dolby TrueHD with Dolby Atmos
Codec ID : A_TRUEHD
Duration : 2 h 24 min
Bit rate mode : Variable
Bit rate : 4 641 kb/s
Maximum bit rate : 7 500 kb/s
Channel(s) : 8 channels
Channel layout : L R C LFE Ls Rs Lb Rb
Ford, even though I am not the OP, thank you for the detailed explanation, I learned something new!
I was just about to post an update similar to what you told me, but you said it better than I would have said it. I hooked up my laptop to my receiver, and when I played the files through the plex media player, I was getting DTS-MA, and Dolby Atmos depending on the file. Is there much of a difference between D+ and DTS-MA from a quality perspective?
The former is a lossy codec
the latter is a lossless codec (actually “DTS HD-MA” is).
Whether you will be able to tell the difference, depends on the size and quality of your surround setup.
And the status of your hearing.
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