[pulseaudio-discuss] How to control the right and left channel for a specific application using CLI ?

[Tanu Kaskinen]

On Wed, 2020-11-04 at 14:56 +0100, 01ivier at labomedia.org wrote:
> Le 2020-11-04 01:17, Arun Raghavan a écrit :
> > On Tue, 3 Nov 2020, at 7:09 PM, 01ivier at labomedia.org wrote:
> > > Le 2020-11-03 23:49, Arun Raghavan a écrit :
> > > > On Tue, 3 Nov 2020, at 5:28 PM, 01ivier at labomedia.org wrote:
> > > > > Hello again,
> > > > > 
> > > > > I want to know if there is a way, still in command line, to control
> > > > > the
> > > > > right and left volumes of an application.
> > > > > With Pulseaudio Volume Control, you can click on the lock icon related
> > > > > to a launched application, and two sliders appear to do so.
> > > > > Is it possible in CLI ?
> > > > > 
> > > > > My goal is to run two applications on the same card, but to assign
> > > > > right
> > > > > channel for one and left for the other.
> > > > > 
> > > > > Possible complication : the output of my application is in mono and
> > > > > with
> > > > > Pulseaudio Volume Control I don't get the two sliders if I click on
> > > > > the
> > > > > lock icon.
> > > > 
> > > > You can use pactl to do this:
> > > > 
> > > >   pactl set-sink-input <sink input index> <volume for channel 1>
> > > > <volume for channel 2> ...
> > > > 
> > > > You can look up the sink input index and channel map for channel order
> > > > with:
> > > > 
> > > >   pactl list sink-inputs
> > > > 
> > > > -- Arun
> > > 
> > > Hello Arun and thanks for the quick answer.
> > > 
> > > It's exactly the command I was looking for.
> > > Unfortunately, as I thought, it doesn't work in my case because my
> > > output is in mono.
> > > Here's what I get:
> > > Failed to set volume: You tried to set volumes for 2 channels, whereas
> > > channel(s) supported = 1
> > > 
> > > I can't change the output of the software.
> > > Is there possibly a way to create a virtual stereo output from the 
> > > mono
> > 
> > Yup, check out module-remap-sink:
> > https://www.freedesktop.org/wiki/Software/PulseAudio/Documentation/User/Modules/#module-remap-sink
> > 
> > -- Arun
> 
> Thank you,
> 
> Your answer is good... I just asked the wrong question... Sorry...
> 
> What could help me, in my case, is to remap the mono sink-input (the 
> ouput of my application) into a stereo one, so that I could control the 
> volume of each channel with set-sink-input.
> Maybe I missed something but module-remap-sink doesn't like to do it.
> 
> I tried to use module-remap-source but "Name or index of the master 
> source" seems to concern sink listed with "pacmd list-sinks" not "pactl 
> list sink-inputs".
> 
> Is there a solution to get a stereo sink-input from a mono one ?

There's no way to change the channel map of a sink input. It sounds
like you could load one remap-sink for the left channel and one remap-
sink for the right channel, and point the application to the
appropriate remap-sink.

-- 
Tanu

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