Plex Media Server always transcodes AC3 5.1 audio to 2-channel AAC when streaming to Roku Ultra

Plex Players Streaming Devices
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My Plex Media Server will transcode the AC3 5.1 audio track of a movie to 2-channel stereo anytime I stream to my Roku player. This is a relatively new development (sometime between late last year and now). I have done all of the testing I can think of, and can’t figure out exactly where the problem is. I have collected some log files and attached them here; hopefully someone will be able to tell me how I can get my surround sound back.

Plex Media Server - version 1.31.2.6810
Roku Ultra - Model 4670X Software version 11.5.0 Build 4312-46
Roku Plex App (Channel) - version 7.0.30.8287
TV - Samsung UN46EH5300 with “Plex for Samsung” App version 2.013

The video used for all of the testing described below was the movie “The Avengers” and it was in MKV format. MediaInfo output Plex XML files are attached.

All devices (Plex media Server, Roku Ultra, TV) are connected by Ethernet cable to the same router.

The Roku Ultra is configured to output Dolby and DTS audio.

When Plex Media Server streams to Roku Plex App, the server dashboard shows that the video is Direct Stream MPEG2VIDEO and that the audio is Transcode AC3 5.1 —> to AAC and the AV receiver plays Stereo.

When Plex Media Server streams to Roku media player using Plex Server DLNA (bypassing the Roku Plex APP), the server dashboard shows that the video is Transcode MPEG2VIDEO —> H264 and that the audio is Transcode AC3 5.1 —> to AAC and the AV receiver plays Stereo.

When Plex Media Server streams to “Plex for Samsung” app on the TV (bypassing Roku completely), the server dashboard shows that the video is Direct Play MPEG2VIDEO and that the audio is Direct Play AC3 5.1 and the AV receiver plays Dolby Digital Surround.

When I copy the movie to a USB drive, plug that drive into the Roku Ultra (bypassing Plex completely), and play the video using the Roku Media Player, the AV receiver plays Dolby Digital Surround.

In the file “Roku Plex App Log - Startup with Channel Info 03-19-23.txt” which is created by the Roku Plex app (when local logging is enabled) there is a section (beginning at time 3/19/2023 16:05:43.287) described as “Channel Info”. If I understand this section correctly, it says that there is no multi-channel audio support in the Roku player which clearly is not the case.

Log files “Plex Transcoder Statistics (Corresponds with Movie Playback Roku Log).log” and “Roku Plex App Log - Movie Playback 03-19-23.txt” show part of the playback process from both ends. The transcoder log starts when playback is initiated. That same point in the Roku app log is almost half way down in the log.

Log file “Roku Media Player Plex Transcoder Statistics.log” shows the playback transcode process from the Plex server end when the movie is streamed to the Roku Media Player (DLNA).

It looks to me like the movie contains a valid AC3 5.1 sound track and that it plays correctly on the Roku Ultra when Plex is bypassed completely. The Plex server will direct play the sound track when streaming to the Plex app on the TV when Roku is bypassed completely. It looks like the problem is with the Roku player but might not be with the Roku Plex app as it looks like the Roku Plex app either isn’t being “told” or doesn’t understand that multi-channel audio support is available.

Plex Transcoder Statistics (Corresponds With Movie Playback Roku Log).log (21.9 KB)
Roku Media Player Plex Transcoder Statistics.log (92.6 KB)
Roku Plex App Log - Movie Playback 03-19-23.txt (175.1 KB)
Roku Plex App Log - Startup with Channel Info 03-19-23.txt (75.9 KB)
The Avengers MediaInfo Output.txt (4.6 KB)
The Avengers 506.xml.txt (22.0 KB)

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If you also only notice this happening with mkv files it has something to do with the settings in the Plex app

If I recall correctly there was a problem with audio syncing and mkv files a long time ago

They introduced a default behavior that transcoded the audio on purpose to make it play correctly

I think you have to check “force direct play” to get it to stop

I want to say there was something else but it was too long ago for me to remember what specific setting it was

Maybe someone who is using one currently knows. As you scroll through the audio settings inside the Plex app you get a pop up explaining the issue if I recall

3

I have a Roku 4800X and I set Force Direct Play and it plays AC3 5.1 just fine thru my Sony receiver. Apparently the Roku has problems with AAC 5.1 and will down it to AAC 2.0. So I converted all my movies from AAC 5.1 to AC3 5.1.

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I want to thank everyone for the suggestions.

The solution to my problem is in the post that JaysPlex7 quoted. When I checked Roku’s audio mode during playback, I found that “Leveling” was enabled. When I disabled it, AC3 5.1 surround sound began working again, and the Plex server stopped transcoding the AC3 5.1 audio down to AAC 2-channel.

I’m not sure how leveling got enabled but it happened within the last couple of months, there are only a few people involved (all though some are less than 12 years old).

In addition to the Plex server now direct playing AC3 5.1, I was able to see in the Roku Plex App log that “Audio Output: Stereo" and “Audio supports surround sound: false” went to “Audio Output: 5.1 surround” and "Audio supports surround sound: true”

Unfortunately “Audio supports multichannel AAC: false” remains, but I’m ok with that as all of my movies are AC3 5.1.

I want to apologize for missing the original post that JaysPlex7 quoted. I had searched the forum for posts relevant to transcode issues, but somehow missed that one.

Thanks again for the suggestions.

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Using two Roku ultras on different TVs…
I changed to ‘FORCE DIRECT PLAY’ and it does indeed direct play 5.1 .
HOWEVER… if there is a video that has AC3 stereo i had trouble with it and had to go back to AUTO.
BUT i also had LEVELING turned on… Tuned it off and AC3 stereo had no issue with the FORCE DIRECT PLAY… interesting…

UPDATE:
this worked on my newer Vizio 42in, BUT on a 8 year old LG 52in… with FOREC DIRECT PLAY enabled, get an error with AC3 audio that no audio available, then reverts back to direct play AUTO

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