Opus quad channel audio downmixed incorrectly

[antoniu200]

Hello,

I have a multitude of Opus files that have quad channel configuration (or videos with such audio stream). Using MPC-HC to open the files, LAV default settings and a pair of (stereo) headphones, I can notice that the 4th channel is inverted.
This problem only appears on Opus quad channel audio streams (or files). AC3 ones do not have this problem.

I have tried versions 0.74.1, 75.1, 76.1, 77.0 and 77.2. The issue appears in 0.77.0, all versions below do not have this issue.

Could you please take a look? If you need some sample, please let me know.
Thank you!

[Nevcairiel]

A sample would be good. I'm not quite sure what "inverted" means in this context.

[antoniu200]

Thank you for the reply!

The issue appears when some options (that might be incompatible with eachother?) are enabled at the same time. Not with just one or the other.
I worked around this issue back in April by resetting LAV Filters, carefully toggling the options I needed and downgrading to 0.76.1.

"Inverted" means inverted polarity.

I will update this issue with a sample and more precise details as soon as I can re-identify the options that triggered this issue, but I remember both had something to do with channel mixing.

[Nevcairiel]

If you use DPL downmixing, that is intentionally causing polarity inversion. Its not useful as a generic downmixer, but only if you have a DPL compatible upmixer at the other end.

[antoniu200]

Okay, I just upgraded to 0.77.2 and made sure to reset all settings.
As soon as I clicked on a Quad-Channel Opus video, the last channel had inverted polarity.

What fixed it was toggling on Mixing - Mixer - Enable Mixing. As soon as I toggled that, the audio was fixed.
I downgraded immediately back to 0.74.1, reset the settings again. Opened the same video, the issue was not present (made sure that Mixing - Mixer - Enable Mixing was not toggled).

I will provide a sample video soon.

If you use DPL downmixing, that is intentionally causing polarity inversion. Its not useful as a generic downmixer, but only if you have a DPL compatible upmixer at the other end.

I believe I am not using DPL downmixing, I am not even sure where I would find it - I haven't seen such option in the menu.

[clsid2]

Look at the channel mask value on the Status tab during playback.
MPC-HC menu > Play > Filters

Quad (front+back) should be 0x33
https://learn.microsoft.com/en-us/windows-hardware/drivers/ddi/ksmedia/ns-ksmedia-ksaudio_channel_config

[antoniu200]

Sorry for the incredibly late reply, so much stuff popped up one after the other that ended up taking all my time.

If you use DPL downmixing, that is intentionally causing polarity inversion. Its not useful as a generic downmixer, but only if you have a DPL compatible upmixer at the other end.

I believe I am not using DPL downmixing, I am not even sure where I would find it - I haven't seen such option in the menu.

Okay, I found a video I can upload here. Problem is, I cannot reproduct the issue anymore.
Where is DPL downmixing found?
I would like to test if enabling this option presents the same symptoms I was describing, maybe it got stuck on, even after settings were reset, and this was the problem all along.

Look at the channel mask value on the Status tab during playback. MPC-HC menu > Play > Filters

Quad (front+back) should be 0x33 https://learn.microsoft.com/en-us/windows-hardware/drivers/ddi/ksmedia/ns-ksmedia-ksaudio_channel_config

I did, it was always 0x33.