[pulseaudio-discuss] How to combine microphone audio and music from application to pipe to video conference

[Joe]

Someone should write a small book on this. I bet it would sell.

Joe

On 5/16/20 1:23 AM, Sean Greenslade wrote:
> On Fri, May 15, 2020 at 11:04:00PM -0400, Samir Parikh wrote:
>> Hello,
>>
>> I am trying to combine the audio from my microphone (either built in
>> microphone from my laptop or bluetooth headset) with music playing
>> from Rhythmbox Music Player running on Ubuntu 16.04 and pipe that as
>> the audio input to video conference services such as Jitsi.
>>
>> I don't know much about Linux audio internals and wasn't sure how to
>> do this.  Can I do this completely via the operating system using
>> Pulse Audio?  Do I need to do something with Jack?  Or do I need
>> specialized software such as OBS, Ardour or Reaper?
>>
>> Any help or suggestions on pointing me in the right direction or how
>> to get started would be greatly appreciated.  I'm hoping that I can do
>> this completely through software without external hardware such as a
>> mixer or something.
> This is definitely possible entirely within pulseaudio. I'll go over the
> basic concepts here, then show an example.
>
> Pulse has two types of sound devices, sources and sinks. Sources are
> input devices like microphones. Sinks are output devices like speaker or
> headphone ports. Programs that work with sound can attach to sources in
> order to pull sound in, and can attach to sinks to output sound. I
> suggest playing around with the "pavucontrol" utility to see what
> sources and sinks are present on your machine. It also shows what
> applications are recording or playing back audio, and allows you to
> redirect existing audio streams on the fly. It's quite handy.
>
> Within pavucontrol, there is a separation between sources and sinks, and
> the two cannot directly be mixed. In order to mix a music sink and a
> microphone source, we'll use a few manually-loaded pulseaduio modules.
> Note that this can easily be scripted once you find the set of commands
> that work well for your setup.
>
> We'll first need to create a "virtual mixer" device. This will receive
> both the music and the voice streams and mix them together. Run the
> following commands:
>
> $ pacmd load-module module-null-sink sink_name=virt_mix
> $ pacmd update-sink-proplist virt_mix device.description=VirtualMixer
>
> Pavucontrol should now list "VirtualMixer" in the Output Devices tab.
>
> Next, you'll need a loopback device to feed your microphone's sound to
> this virtual mixer. Run this command:
>
> $ pacmd load-module module-loopback sink=virt_mix
>
> In pavucontrol, go to the Recording tab and change the Show dropdown to
> All Streams. There should be an entry titled "Loopback to VirtualMixer"
> with a dropdown to select the loop input. Pick the appropriate input
> that corresponds to your microphone.
>
> Now you can begin playing music, and in the Playback tab of pavucontrol
> move the music playback to the VirtualMixer.
>
> Finally, begin recording / using your conferenece application. In the
> Recording tab of pavucontrol, find the entry for the recording
> application / conference application. Change its microphone to "Monitor
> of Null Output", which is the virtual source that pulls from the
> virt_mix sink. Verify that it is behaving the way you want.
>
> Hopefully this isn't too confusing. Feel free to ask for clarification
> if needed. I've set up a number of complex audio workflows in linux,
> some of which took a lot of experimentation to get working well.
>
> --Sean
>
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