Plex Server Version#: 1.28.0
Plex Player Version#: Plex for LG, client 5.43.2, platform 7.1.0
Television Version#: LG OLED77G2PUA
Receiver Version#: Onkyo TX-NR646
With DTS (DCA) on the client enabled, some media with DTS will not play, yet others will. I haven’t been able to figure out why. I have an LG TV and am using optical out to an Onkyo TX-NR646. On the Onkyo, I have set the audio to “direct”. If I uncheck DTS (DCA) on the client, audio plays for those problematic files. I assume Plex does a conversion on the fly because the file only has DTS audio. I’d like to understand why DTS doesn’t play from some files, yet it does on others. Also, could I do something with MKVToolNix to correct the issue? It is very unlikely a Plex issue, but any helpful information would be greatly appreciated.
Current LG TVs do not decode or passthrough DTS audio formats (they dropped support several years ago). Check the specifications for the TV. DTS is not listed. The review at rtings.com provides further details.
Do not check the box to enable DTS audio in the Plex LG app. The box is visible, but unchecked by default for LG TVs that do not support DTS. If checked you will most likely see inconsistent results.
When you play media with DTS audio, Plex Media Server should transcode it to a supported format.
Monitor playback via Plex Dashboard → Now Playing. It will show if Plex Media Server is transcoding the video or audio, and to what formats.
If possible, connect the tv to the receiver using the HDMI-ARC ports on both units.
It will not help with DTS audio. However, it will pass formats not supported by optical, such as PCM 5.1 and Dolby Digital Plus 5.1 + Atmos (used by Netflix/Amazon/etc streaming services). Optical audio is limited to PCM 2.0, AC3 5.1 (and DTS 5.1 for devices that support DTS audio).
This will also enable you to use CEC control. Powering on the TV should also power on the receiver. Volume up/down/mute on the TV remote should control the volume on the receiver.
If you have a TV that still supports DTS, also check what type of DTS is in the file. There are many variations of DTS and your TV may not support all of them.
I don’t want the TV to process the audio at all and simply pass it to the Onkyo receiver. Since I have selected in the TV configuration to send audio to Optical out, I think that it is simply treating it like a passthru. Isn’t that correct? I assume that it is because DTS does work for some files. If the TV was trying to process the audio, there would be no sound because it doesn’t support DTS.
Using the Plex dashboard, I found that the file that works has audio of DTS-HD MA 5.1 (via direct play). It turns out that the file that does not work has exactly the same audio according to Plex.
I used MediaInfo to look at the audio of the files. The one that does not work
Audio
ID : 2
Format : DTS XLL
Format/Info : Digital Theater Systems
Commercial name : DTS-HD Master Audio
Muxing mode : Header stripping
Codec ID : A_DTS
Duration : 1 h 56 min
Bit rate mode : Variable
Channel(s) : 6 channels
Channel layout : C L R Ls Rs LFE
Sampling rate : 48.0 kHz
Frame rate : 93.750 FPS (512 SPF)
Bit depth : 24 bits
Compression mode : Lossless
Language : English
Default : Yes
Forced : No
The one that does work:
Audio #1
ID : 2
Format : DTS XLL
Format/Info : Digital Theater Systems
Commercial name : DTS-HD Master Audio
Codec ID : A_DTS
Duration : 1 h 35 min
Bit rate mode : Variable
Channel(s) : 6 channels
Channel layout : C L R Ls Rs LFE
Sampling rate : 48.0 kHz
Frame rate : 93.750 FPS (512 SPF)
Bit depth : 24 bits
Compression mode : Lossless
Title : Surround
Language : English
Default : Yes
Forced : No
Would this be a problem? I can’t find any other difference.
Muxing mode : Header stripping
As mentioned in my first reply optical is much more limited than HDMI-ARC.
No matter which connection you use, do not select DTS audio in the Plex app settings.
I do not know why you hear audio for some DTS tracks. The TV may be converting it to another format such as PCM. The Onkyo should be able to tell you what audio format it is receiving from the TV.
as stated above, newer TVs not only no longer decode DTS audio, but also don’t passthrough DTS anymore
The capabilities of a SPDIF or TOSlink connection are not sufficient for the newer and higher quality audio formats.
Forget about passing through DTS-HD MA or Atmos over such a connection in general.
I determined that the ones that are playing have a second track that is not DTS. Plex is likely choosing this to play. Unchecking the DTS (DCA) in Plex gets the audio to play for the ones that didn’t have a second track. Does Plex do a quick conversion from DTS to something else? If so, to what? Should I manually convert these files to AC3 or should I allow Plex to do the conversion on the fly?
I have set up the HDMI (ARC) connection so that I am no longer using optical.
You should be able to see this in the Dashboard of the web app, during such a playback on the TV.
If your server has plenty of processing power, it can do the on-the-fly conversion.
If you want to save on power, pre-convert the audio to either AAC stereo or AC3 (the oldest Dolby digital variety).
The Dashboard says it is converting it to AAC. But, how many channels and what bit rate? It doesn’t show this.
It seems to me that I should convert the DTS files to AC3 (5.1 channels, 448K) rather than AAC (5.1 channels, 384K) since AAC has a lower maximum bitrate. I’m using Box4 Movie Re-Packager and these are the best options available.
It can copy the video stream unaltered and transcode the audio to desired format.
If transcoding to AC3, use 640kbps, the max bitrate for AC3.
Also consider EAC3, the successor to AC3, at 640kbps or 768kbps. Netflix streams EAC3 at 640kbps and EAC3 + Atmos at 768kbps (Engadget).
Pull the log files. Look in Plex Media Server.log (or .1 to .5) for a line containing Reached Decision.
Example: Transcoding media to fit 2 Mbps bandwidth limitation. Audio transcoded to Opus 2.0 at 206kbps (at the end of the entry). Aug 09, 2022 19:17:36.625 [16124] DEBUG - [Req#528/Transcode] Streaming Resource: Reached Decision id=72233 codes=(General=1001,Direct play not available; Conversion OK. Direct Play=3001,Not enough bandwidth for direct play of this item. Required bandwidth is 5733kbps and only 2000kbps is available. Transcode=1001,Direct play not available; Conversion OK.) media=(id=264715 part=(id=266150 decision=transcode container=mkv protocol=hls streams=(Video=(id=566212 decision=transcode bitrate=1697 encoder=h264_nvenc width=720 height=302) Audio=(id=566213 decision=transcode bitrate=206 encoder=libopus channels=2 rate=48000))))
My setup: LG B7 OLED ← HDMI-ARC → Denon AVR-X4300H
I disabled DTS in the Plex app (my TV is old enough to support DTS), then played a movie with DTS-HD MA 5.1 audio and another with TrueHD + Atmos 7.1 audio.
Plex Media Server transcodes DTS-HD MA 5.1 to AAC 5.1 at 774kbps. The TV or Plex app seemingly converts this to EAC3, as the display on the Denon reads Dolby Digital Plus with 5.1 channels.
Plex Media Server transcodes TrueHD 7.1 to EAC3 7.1 at 1032kbps (Atmos lost in the process). This is delivered to the Denon as EAC3 5.1. No idea what happens to the two channels not delivered to the receiver.
I have found that the Optimize option in Plex server will convert these DTS files without an external program. Selecting “Original Quality” was best for me as it converted the DTS to a high quality AAC, but kept the video mostly the same.
