You need to select “Optical Output” in the Plex App.

Thanks, but I can’t find this option anywhere on my TV’s Plex app. I don’t think it has this. 

This link may help.

Thanks

I had seen this after your first reply, but assumed those settings just related to the player for Mac rather than any player that I use. I’ll have a look shortly. Hopefully this works!

Edit: as I suspected, the settings you have linked only relate to the desktop player apps.

Last I checked Sonos do not support PCM 1.0: https://support.sonos.com/en-us/article/supported-home-theater-audio-formats

You need to transcode to PCM 2.0.

How do I do this? Does this mean I need to change my files with something like handbrake? It sounds like something I was hoping to avoid..!

Transcoding is rarely a problem, pick a tool that does mass conversions and feed it your whole library. Let it run overnight and it will likely finish by morning.

Once converted archive your original files and move the transcoded ones into their previous location. Reindex the Sonos library tool.

I have had to transcode a few things, usually going to a lower encoding level that Sonos supports and it has never been an issue.

You shouldn’t need to change any files, my understanding is that Plex transcodes live, and PCM 1.0 to 2.0 is about the simplest transcode I can think of.

By this point, I’m fairly confused. 

I’ve had a different answer from almost everyone on this. You’d think it would be straightforward. 

I’m still puzzled why this expensive equipment cannot play my mono files. I’m thinking… does other home theatre audio equipment have this problem? If I go and buy a Samsung soundbar and surrounds, will that have this problem? I’m wondering if the Apple TV 4K will change anything here, doing some kind of automatic conversion. The whole issue is just really weird. How simple it is, yet how few people know, how few perspectives I’m getting on it, how different the answers are. 

Just all feels very odd. 

As said before, take a look at your Plex server settings.

so, this was completely incorrect advice.

nowhere on that page does it reference PCM 1.0 and PCM 2.0 and at no point have i stated my problem relates to those two things that i don’t know what they are.

hmm, you advised me to transcode my files, but apparently i don’t need to do that!

you, also, have referred to PCM 1.0 and PCM 2.0 and i’m sure my problem related to mono audio files not playing sound! it gets weirder! 

someone incorrectly advised me to look at the settings for the mac player app. they was incorrect advise because this doesn’t relate to the mac player app. so, no-one has said anything before!

so basically no-one has a clue what they’re talking about!

Hi ​@brokenboxes 

Welcome to the Sonos Community!

Sorry to hear of this issue you are having with playing movies with mono sound tracks.

We’d like to look into this for you - could you please supply us with the names of some example movies that you are unable to watch? Hopefully, we’ll be able to find some online with the same audio tracks.

If you can find the same movies online, please try playing them there rather than with Plex and let me know if there are any differences in results.

I look forward to hearing back from you.

You may be able to avoid doing a mass transcoding but it would solve your problems.

several hundred of my films are in mono, but the one i watched last night was this one:

https://www.criterion.com/films/27525-the-night-of-the-hunter

“New digital transfer made from 35 mm film elements restored by UCLA Film & Television Archive in cooperation with MGM Studios, with funding provided by the Film Foundation and Robert Sturm, with uncompressed monaural soundtrack”

I see the answers in this thread as advice about where you could try for a solution, rather than a supplying a solution. 
 

The page https://support.sonos.com/en-us/article/supported-home-theater-audio-formats mentions Stereo PCM, that could be the PCM 2.0 that is being talked about here. More on PCM you will find here https://en.wikipedia.org/wiki/Pulse-code_modulation

​@brokenboxes, 

As per the attached screenshot, the transcoder on the Plex server works automatically and so if it’s not transcoding your movie audio automatically then yes you do need to convert the movie files to get them to play in a compatible Sonos Home Theatre audio format as stated here:

https://support.sonos.com/en-us/article/supported-home-theater-audio-formats

Handbrake is perhaps worth a try to see if that might work for you.

Never mind.

It remains a mystery if the Apple TV 4K can convert from mono to stereo PCM. Who knows. I guess I’ll find out when it arrives tomorrow. If not, I’ll have to re-acquire the films in question from a different source and be a bit more careful with the audio format.

I’ll not bother with converting, though appreciate that is one solution. 

I received my new Apple TV 4K today. After setting it up and playing the above film and several others with mono audio, there is no longer a problem. The Apple TV 4K seems to convert any audio to multichannel LPCM. Problem solved.

Glad I didn’t spend hours tinkering with Plex settings, or transcoding my whole library, eh!

Hi ​@brokenboxes 

Welcome to the Sonos Community!

I am glad to hear that upgrading your Apple TV fixed this issue for you. Thanks for updating the thread!

I had just obtained a version of “The Night of the Hunter” to play on Plex, but only the commentary was in mono AAC. As it took me a while to get it, I figured I’d share my findings anyway:

It did play, and I could hear the audio. Looking at my Sonos app, Stereo PCM was reported. I assumed this is because my TV output format is set to Auto, so I tried Passthrough instead, but I still see Stereo PCM reported. I presume this is because the communication between the devices is informing the Plex app that the AAC codec is not supported by the audio device, so Plex is converting to PCM. Something, somewhere is doing the conversion, anyway. I was testing on a nVidia Shield Pro, but I have Dolby conversion off, so I don’t think it is the system doing the conversion. In terms of Audio, my Plex settings are at their defaults.

Long story short, Sonos Home Theatre devices do not support the AAC codec via HDMI/Optical - only when streaming or playing from Music Library. To play a movie with such a sound track, conversion must be performed at some point in the playback chain to a supported format.

I do now wonder if there was a way to do it with your older Apple TV.

“Long story short, Sonos Home Theatre devices do not support the AAC codec via HDMI/Optical - only when streaming or playing from Music Library.”

All my movies have AAC audio and play fine; it’s just the mono ones that wouldn’t play. Also, AAC is supported by Sonos according to the documentation.

“I do now wonder if there was a way to do it with your older Apple TV.”

I didn’t have an older Apple TV, was just using the plex app on the Samsung TV. Either way, it now works, I’m not exactly sure on what was going on technically that prevented it.