Linux puskom-ProLiant-DL385-Gen10 5.4.0-150-generic #167~18.04.1-Ubuntu SMP Wed May 24 00:51:42 UTC 2023 x86_64

//usr/share/doc/libasound2-plugins/vdownmix.txt

 VDOWNMIX PLUGIN
===============

The vdownmix plugin is a downmixer from 4-6 channels to 2-channel
stereo headphone output.  This plugin processes the input signals with
a simple spacialization, so the output sounds like a kind of "virtual
surround".

For example, define the below:

	pcm.!surround51 {
		type vdownmix
		slave.pcm "default"
	}
	pcm.!surround40 {
		type vdownmix
		slave.pcm "default"
	}

and the outputs from video player to these PCMs are converted to the
default 2.0 output with a proper downmix.

The accepted format is currently only S16.