[pulseaudio-tickets] [Bug 94563] New: Option to minimally upmix or remap "mono" channel only (for speaker configurations greater than 2.x)

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=94563

            Bug ID: 94563
           Summary: Option to minimally upmix or remap "mono" channel only
                    (for speaker configurations greater than 2.x)
           Product: PulseAudio
           Version: unspecified
          Hardware: Other
                OS: All
            Status: NEW
          Severity: normal
          Priority: medium
         Component: daemon
          Assignee: pulseaudio-bugs at lists.freedesktop.org
          Reporter: freedesktop at nuclearsunshine.com
        QA Contact: pulseaudio-bugs at lists.freedesktop.org
                CC: lennart at poettering.net

At present, PA's remix logic seems to work well for 2.0 speaker configurations:

* Mono is upmixed to each channel (so its apparent origin for a person in front
of the speakers is front/centre
* Stereo goes to the relevant channels
* 5.1 etc. are downmixed to the left and right channels - centre is mixed to
both, etc.

It doesn't work well for 5.1 speaker configurations:

* Mono is upmixed to all channels, instead of either front-left+front-right or
centre only (so its apparent origin for a centrally positioned user is in their
head, more or less, instead of front/cenre)
* Stereo is upmixed to all channels, instead of being mapped to front-left and
front-right (this happens even with a sink input with "channel map:
front-left,front-right)
* 5.1 goes to the correct channels. Not 100% sure about 7.1 etc.

If remixing is disabled with a 5.1 speaker configuration:

* Mono audio (sink input with "channel map: mono") is discarded entirely
* Stereo goes to front-left and front-right
* 5.1 goes to the correct channels. Presumably additional channels from 7.1
etc. are lost.

Applications such as Firefox appear as a mono sink input when playing back mono
audio (of which there are many examples on the web, for instance many YouTube
and Twitter videos and probably many more). At present a PA user has to choose
between one of:

* No audio output in these cases (and other applications presenting a mono
source), or
* Both mono and stereo audio being upmixed to *all* channels, or
* Continually switching PA's speaker configuration from 2.0 to 5.1, or
* Continually toggling PA remixing.

A presumably fairly easy fix so 5.1 users could avoid this would be an option
to remap the "mono" channel to "centre". Another would be to have the option to
upmix mono to front-left+front-right.

Note, this is not the same as bug 39360, which started as a request to have
auto-switching of PA speaker configuration, and evolved into a request for more
sophisticated "least-necessary" remixing.

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