Playing local multi-channel audio (eg LPCM 5.1 .flac files)

Yes, that’s how I understand it, and why the Google TV (nor the TV) will not be able to send the uncompressed multi-channel audio.

I was hoping there’d be a format I could have on my home network that the Beam could play directly - I think that it can it play multi-channel audio files from streaming services - do they use a particular sound format?

I think that not having eARC is going to annoy me :/

The only 5.1 format that is going to work over ARC (or S/PDIF) is Dolby Digital 5.1.

Its unlikely you can re-encode your PCM 5.1 to that (because Dolby licenses) but you may be able to re-rip the file to DD 5.1 if it is already in that format on the optical disc.

That was a big rabbit hole. I can now send surround versions of my music straight to my Sonos Beam gen 2 through my home network. Here is what I learned:

Short version: If I could have extracted a 640kbps pre-encoded Dolby Digital stream then I would have put that in a .mp4 (or .4a) file and used that. I only have a Beam gen 2 soundbar to play back through. The sound was different, maybe a bit more “stereo” than playing standard stereo files of the CD version. Because the 5.1 channel files play back so much louder (when streaming) than standard 2-channel .flac files I won’t be able to use them in a playlist.

Long version:

The advice to extract an existing Dolby Digital encoded stream was good, except I’m sure there was no DD track for the album on my Bluray disk (Marillion Misplaced Childhood Deluxe Edition), despite having the DD logo on the box.

I extracted the compressed DTS core, but I can’t find any way to send that to the Beam soundbar whatever file/container format I wrap it in. Even when I plugged my bluray player back in I still couldn’t find a way to play the compressed DTS track to the Beam - maybe because 1509kbps is too much for ARC, or maybe because my TV doesn’t pass through DTS?

The advice to use .mp4 files was helpful because multichannel .flac and multichannel .aac cannot be played: the 5.1 .flac is rejected with a message in the app; a 640kbps multi-channel .aac looks like it’s playing in the Sonos app, but the sound is silent and I need to cut the power to the Beam and reconnect before I can stream any other content! 

I also tried putting a lossless TrueHD audio stream in a .mp4 file, but although the Sonos app lets me add it to the queue there is an error shown when the track is played back. (And, I only have HDMI-ARC, not eARC, so I can’t send TrueHD through the HDMI connection to the Sonos.)

So, to re-encode the 96kHz/24-bit audio from the disk there were two codecs that worked: ac3 (as used in Dolby Digital) and eac3 (as used in Dolby Digital Plus). I only have the free ffmpeg tool to encode them, and it is not as good as commercial/professional software at encoding e/ac3, but is competent at high bitrates. The eac3 codec allows much higher bitrates than ac3, but ffmpeg has a reputation for generating invalid eac3 streams, and eac3 players are often unable to cope with eac3 errors. I definitely managed to make some files that cause the Beam to go silent part-way through playback.

After a lot of trial and error and reading, and in case I need to look it up again in the future, here is the command I used to make a multi-channel file that I can pick from the Sonos app and play directly over my home network:

ffmpeg.exe -i "TrackOne.flac" -vn -c:a eac3 -b:a 1024k -af aresample=out_sample_rate=48000 -cutoff 20000 -movflags +faststart "TrackOne.m4a"

(I used ffmpeg v7.0)

When the 5.1 channel .m4a file plays back over the network (when I choose the track in the Sonos app) the sound is very loud - much louder than any other source, and much louder than streaming the same file via my Google TV to the Sonos via HDMI-ARC.

I guess any of this could change with new firmware in the future, but maybe interesting to someone...🤷‍♀️

Aha - yes - I can specify the loudness of the input file when I create the .mp4 audio file: “Dialog Normalisation”. It was originally intended so that film and tv dialog could be played back at a consistent level in different programs, but it is used to keep music at a consistent level in Atmos playback too. The number is added to the audio stream and then the decoder (my Sonos soundbar) drops the volume so that I don’t have to reach for the remote control so often.

My command needs to look like this:

ffmpeg.exe -i "TrackOne.flac" -vn -c:a eac3 -b:a 1024k -af aresample=out_sample_rate=48000 -cutoff 20000 -dialnorm -3 -movflags +faststart "TrackOne.m4a"

I used “-dialnorm -3” in that example. The range is from -31dB (which effectively tells the speaker not to turn down the volume at all) up to -1dB, which indicates the audio is very loud and the volume should be turned down by 30dB. When I didn’t give any value then ffmpeg.exe added a default value of -31 which is sometimes helpful, but on my Beam Gen 2 meant the volume was way too loud.

Technically I should measure the “integrated loudness” of the input file (or maybe the whole album) in LUFS and then give the value as “dialnorm”. In practice my 2 music blurays were -11 and -14; the encoded .mp4 files still play back louder than my CDs. Using -3 in the encode seems to match the volume of my CD rips when I’m streaming the files from my local network, but plays back quieter than Atmos files played back from my Amazon Unlimited trial. 

The playback volume through the HDMI input is different, but I guess that’s a different problem.

Learning way more than I need to about Dolby Digital Plus, there are a few extra parameters that might be helpful to specify in that command:

-dmix_mode 2 -loro_cmixlev 0.707 -loro_surmixlev 0.707 -ltrt_cmixlev 0.707 -ltrt_surmixlev 0.707

I didn’t hear them make any difference to the playback on the soundbar though.