7.1 channel surround work around

[guykuo]

Hopefully this work around save others some time. Channel assignment issues have cropped up on VLC periodically over the years. This is not a current problem for 5.1 audio, but 7.1 is definitely a problem.

MacOS coreaudio on my Mac Mini running Catalina is prevented by Apple from passing raw 7.1 surround audio via HDMI. Hence, selecting a 7.1 channel audio track will not work properly with audio device HDMI (encoded). It does pass the raw data stream for Dolby 5.1 and DTS core tracks. Without the below work around, I was only getting two channel PCM audio when 7.1 channel soundtracks were selected in VLC. BTW, you cannot do 7.1 via toslink.

Apple coreaudio will decode up to 8 channels audio and output as 8 PCM audio channels via HDMI. It will only decode 8 channels of audio and is limited to 96 KHz bitrate. So, lossless DTS and true Atmos are not possible. However, 7.1 Dolby and DTS surround can be done successfully.

1. Use the Apple utility/Audio MIDI Setup.app to set HDMI for 8 channel output. You will need to turn on, connect your AVR receiver, and select your Mac as the receiver's input BEFORE doing the Midi setup.

I use 8 channel 24 bit 96 KHz
Configure your speakers in Midi Setup as 7.1 rear surround.
Do NOT remap the channels. Leave them sequentially assigned as default. VLC won't play back the channels in the correct speakers, but we will fix that in VLC. Don't fix it in Midi Setup or you will mess up all other app's audio channel assignments.

2. Configure VLC's channel mapping to place the channels in the correct speakers. (as of vlc-3.0.9-20200219-0454.dmg, the default VLC channel mapping is scrambled when playin 7.1 through through a Denon Atmos capable receiver.

Preferences/show all/audio/filters
Turn on audio channel remapper in the main filter pane.
Setting remap filter to the following got VLC to play channels in correct 7.1 speakers for me.
Output in brackets is what should be selected in the pop up menu0

Left [Left]
Center [Side left]
Right [Right]
Rear left [Center]
Rear center [rear center]
Rear right [Low-frequency effects]
Side left [Rear left]
Side right [Rear right]
Low-frequency effects [side right]

If the above isn't correct on your receiver, you can test by setting all the channels to LEFT, except the center. Change the center from output channel to channel to determine which speaker is played by that labeled output channel. Unfortunately this is very tedious because you must save the setting, relaunch VLC, and reselect audio track for each trial.

During VLC playback, selecting 7.1 track with audio output device --> system sound output device should provide your AVR with multi-channel PCM 8 active channels. Set your receiver to desired processing mode if you wish to upmix to 7.1.4 height effects.

Apple purportedly is supporting Atmos in 2018 and later machines, but I do not have one for testing whether that means coreaudio will pass raw 8 or 12 channel audio without conversion to PCM.

[guykuo]

One other gotcha.... The Mac is likely to refer to 2 channels if it ever goes to sleep or receiver is set to HDMI pass through while on standby.

If Mac Mini is kept awake (I use Ampehtamine) and receiver renegotiates the HDMI connection upon coming out of standby, 8 channel setup is more likely to be retained. Pass through HDMI on receiver standby seems to renegotiate as two channels and does not revert back to 8 channels. My advice is to keep AVR receiver HDMI pass-through during standby turned off.

[jb33]

Hi guykuo,
I ran into exactly the same issue today.
Mac Mini with VLC and a Denon Receiver.

I usually use Plex so havent had the problem until today, your instructions solved my problem.

Thanks heaps !