Troubleshooting - 5.1 system receiving 7.1 content and buffering or not playing

Plex Players Streaming Devices
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Server Version#: 4.112.0
Player Version#: 9.27.1.2953

Running Plex Server on Windows PC.
Plex client on Fire TV Stick 3rd Gen (not 4K) plugged into an HDMI port on Denon AVR-X1700H
Denon is setup in 5.1, though I hope to add extra speakers and go 7.1 or Atmos at some point

Media files stored as MKV’s with English only Audio sources and only forced subtitles.

Network includes gigabit connected to PC, Google Home Mesh network for the FireTV stick.

The problem: When a media file contains both 7.1 and 5.1 audio, the server is DirectPlaying 7.1 audio. I assume this is because both the FireTV Stick and the Denon receiver support 7.1, even though I’m not setup as 7.1… This leads to one of two issues, either lots of buffering until I change the audio in the player to the 5.1 stream, then it play flawless, or it never starts playing and changing the audio stream at this point doesn’t help…

I searched and saw lots of refences to 4K 7.1 and TrueHD having issues, but in my case, until I get a 7.1 setup, I want it to switch to play the 5.1 stream, unless the 7,1 stream is okay to play and the receiver should handle the 7.1->5.1 conversion, then I want to eliminate the buffering on 7.1…

Any thoughts or additional info needed?

Thanks,
J.

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Short Answer: If you want 7.1 audio, get a Nvidia Shield Pro. Especially if you want TrueHD + Atmos or DTS-HD MA / DTS:X.

FireSticks cannot passthrough either TrueHD or DTS (all formats) audio. TrueHD is transcoded by Plex Media Server. DTS is converted by the FireStick to Dolby Digital Plus.

In my testing, FireSticks do not output any 7.1 audio (at least when running the Plex app).

Note: The Amazon Cube v3 will passthru TrueHD + Atmos. However, for DTS, it passes only the lossy 5.1 core.


Longer Answer: Can’t help with FireStick 3rd Gen specifics, as I don’t have one. Here’s some tests I ran with FireStick 4K, 4K Max, & Nvidia Shield Pro.

FireStick 4K, 4K Max, and Nvidia Shield Pro are connected to HDMI inputs on a Denon AVR-X4300H.

The Nvidia Shield Pro direct played all audio formats. It delivered AAC 5.1/7.1 as PCM 5.1/7.1 to the Denon. All others were bitstreamed (passthru) to the Denon. Shield has Plex app v9.29.0.3347 & passthru = HDMI.

The FireSticks have Plex app 9.27.1.2953 (current in Amazon store). Plex app HDMI = Passthru. FireStick audio = Best Available.

Neither FireStick delivered 7.1 audio to the Denon. The Left Surround and Right Surround channels were either combined with the Left/Right Rear Surround channels or simply dropped.

Note: Direct Play / Direct Stream / Transcode describes what happens with Plex Media Server. The Plex client, such as the FireStick, can convert the stream to another format. If this happens, the Plex Media Server will have no knowledge of the conversion, and it will not be reflected in the Plex Dashboard or Plex Media Server logs.

AAC 5.1  Direct plays.  Delivered as PCM 5.1 to Denon.

AAC 7.1  Direct plays.  Delivered as EAC3 5.1 to Denon.
    4K: Left Surround combined with Left Rear Surround.
        Right Surround combined with Right Rear Surround
    4K Max:  Left Surround and Right Surround dropped.  No audio.

EAC3 5.1  Direct plays.  Delivered as EAC3 5.1 to Denon.

EAC3 7.1  Direct plays.  Delivered as EAC3 5.1 to Denon.  
          LS combined with LRS.  RS combined with RRS.

TrueHD 7.1  Transcoded to Opus 7.1. Delivered as EAC3 5.1 to Denon.
    4K: LS combined with LRS.  RS combined with RRS.
    4K Max:  LS & RS dropped.

DTS-HD MA 5.1  Direct plays.  Delivered to Denon as EAC3 5.1

DTS-HD MA 7.1  Direct plays.  Delivered to Denon as EAC3 5.1
   Both: LS combined with LRS.  RS combined with RRS.
Unable to cast to Rasplex clients
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At least with Apps - like Plex - which are using the Android Api. And even then there are still some Problems with a few configurations (like many Samsung soundbars are not discovered as being able to play TrueHD)

BUT other apps which are not using the official Way - like Kodi since Kodi 21 (Omega) Alpha 2 you can passthrough TrueHD ofc with ATMOS and also the “complete” DTS. Like DTS:HD MA and X

4

Very good information, thank you for the explanations! The latest plex app update on the fire tv stick seems to have resolved the issue I was having. From what I’ve tested, the 5.1 source is now being played, but these are from sources I’ve played (but finished) before. Next time I get I new movie I’ll double check it.

But very good to know about 7.1. Guess I should check out the Nvidia Shield Pro, perhaps during Black Friday / Cyber Monday…

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