Cannot play multichannel AAC file

Core Machine (Operating system/System info/Roon build number)

Roon Core 1.7 (710) is running on a Synology DS916+ without other issues

Network Details (Including networking gear model/manufacturer and if on WiFi/Ethernet)

Core and all clients are connected via Ethernet (1Gbit lines)

Audio Devices (Specify what device you’re using and its connection type - USB/HDMI/etc.)

smsl m500 vial usb to an iMac running Roon client 1.7 (710)
Denon AV Receiver connected via HDMI to Roon Rock running on NUC10I3
The issue is not related to the endpoints

Description Of Issue
I have some ac3 raw files I captured as transport stream from digital radio. This format is used by German broadcasters when they broadcasts multichannel recordings from classical concerts via SAT Radio. I used ffmpeg to extract the ac3 files from the .ts file

This resulted in ac3 files with the following attributes
Input #0, ac3, from ‘bruckner_4.ac3’:
Duration: 00:22:28.03, start: 0.000000, bitrate: 448 kb/s
Stream #0:0: Audio: ac3, 48000 Hz, 5.0(side), fltp, 448 kb/s 24bit

please note the this is a 5.0 and not a 5.1 multichannel file. This is rare and I only see this from the German broadcasters ‘Bayerischer Rundfunk’ (BR) and ‘Norddeutscher Rundfunk’ (NDR) in their concert recordings.

According to your multichannel information Roon is supporting AAC for multichannel audio files but not AC3. Due to the fact that this is already a lossy format it makes no sense to create huge FLAC files an therefore I converted the ac3 file to AAC resulting in

Output #0, ipod, to ‘bruckner_4a.m4a’:
encoder : Lavf57.83.100
Stream #0:0: Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, 5.0(side), fltp, 325 kb/s
encoder : Lavc57.107.100 aac
size= 53800kB time=00:22:28.03 bitrate= 326.9kbits/s speed=21.9x
video:0kB audio:53552kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.463152%

This file is shown in macOS finder as
Bruckner_1_m4a Apple MPEG-4-Audio 48,9MB sampling rate 48khz channels 5 and plays perfectly outside Roon directly on the Mac.

When I add this m4a file to Roon the file is recognized but Roon reports only 2 channels:
Source: local
Format 326kbps AAC
sampling rate 48kHz
channels 2ch

and does not play the file but skips to the next after a couple of seconds

I need your help to convert the ac3 5.0 multichannel files in a way that Roon is accepting the files. FLAC is no option because this results in huge files.

kind regards

Hi @Christoph_Luebbe,

You can use ffmpeg to do the down-mixing for you:

ffmpeg -i "<input_file>" -ac 2 "<output_file>"

Where the -ac value specifies the number of audio channels desired in the target, 2 in this case. This post has more details and even ways that you can adjust the mix levels:

While the examples are 5.1 the principles hold.

Good luck.

Thanks Carl,

I might be misunderstood here. I want to play theses 5.0 multichannel files via hdmi on my surround system and therefore need Roon to deal correctly with 5.0 encoded AAC files.


Ahhh, I can be a little hard of understanding at times :wink: That’s a different problem and I’m not sure my help will do what it says on the tin, i.e. help. I hope you get this sorted.


Hi @Christoph_Luebbe,

Can you please upload a few examples of such files to Dropbox / Google Drive / etc. and send me a link via private message (click my name -> message)?

done. Thanks for jumping in