Ubuntu – How to create a virtual audio output and route it in Ubuntu-based distro

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I am on elementaryOS 0.4.1 Loki, which is based on Ubuntu 16.04.1.

I want to use OBS, a screen recorder, to record gameplay along with the sounds that come from the same video game. I also want to use a voice chat application in the background while playing the game, but I do not want any of it recorded by OBS.

OBS can't selectively ignore the audio of certain programs, but it can record sound from a specified input device.

I want to create a virtual input and use pavucontrol's output list to route my voice chat application to that input so it's not picked up by OBS. At the same time, I want this input to play back to a headphone/line out port.

I know this can be done in Windows with software such as Virtual Audio Cables, but I don't know how to do the same thing in Linux.

I already attempted to do something with sudo modprobe snd-dummy but it doesn't let me route the dummy to a headphone output.

How should I approach this?

Best Answer

Let me repeat: A single program or group of programs A (game) should output sound both to OBS and the headphone, while another single program or group of programs B (voice chat) should only output sound to the headphone, all on the Pulseaudio level. Correct?

Don't use snd-dummy, it works on the ALSA level. Instead, create a "null sink" on the Pulseaudio level:

pacmd load-module module-null-sink sink_name=game_sink sink_properties=device.description=Game-Sink

Use pavucontrol or, if it can do that, the sound configuration of elementary OS to switch all group A sound outputs to that sink. Each sink in Pulseaudio comes with a corresponding "monitor" source (you can see those in the OBS menu you included), so setup OBS to record from "Monitor of Game Sink".

That takes care of recording from group A only, but doesn't output it to the headphones. For that, you need a loopback from the mentioned monitor source to the headphone sink:

pacmd load-module module-loopback source="game_sink.monitor" sink="your-headphone-sink"

You can find out the names of all sinks, including the headphone sink, with

pacmd list-sinks | grep name:

Leave out the angular brackets when using the names as arguments.

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Debian – How to enable both built-in audio output and HDMI audio output with PulseAudio

I just managed to configure exactly this thanks to the instructions in the ArchLinux wiki :

Set the one sink - HDMI - in pavucontrol/Configuration, and the other - analog output - you specify in default.pa :

load-module module-alsa-sink device=hw:0,0
load-module module-combine-sink sink_name=combined
set-default-sink combined

Maybe you were missing the last two lines?

Addendum: This is OK to add the analog output to HDMI, but what if you want it the other way around? (I want to keep analog input, Pulse calls that "duplex"...) Unfortunately, load-module module-alsa-sink device=hw:0,3 did not work to add HDMI output to Pulse's "Analog Stereo Duplex" configuration. Pulse would start, but no HDMI output.

I compared the output of pacmd list-sinks in the two situations. When I added device=hw:0,3, that one would show up without ports. When HDMI output was chosen in pavucontrol, there would be ports. Looking at the output details, I came up with device=hdmi:0.

Choose "Analog Stereo Duplex" as your pavucontrol configuration, and add to default.pa :

load-module module-alsa-sink device=hdmi:0
load-module module-combine-sink sink_name=combined
set-default-sink combined

Works like a charm. I keep my microphone input, and on pavucontrol/Output Devices I have all options for analog output and for HDMI.

Route application’s audio output to multiple playback devices

If you are using Pulseaudio anyway, have a look at Pulseaudio's modules, in particular module-loopback and module-null-sink. In my experience, snd-aloop is a bit of a pain to use, and as Pulseaudio mostly deals with sound stream transport, it's much easier in Pulseaudio.

So if the use case is "record output of one app in the background, use loadspeakers in the meantime for other stuff, occasionally listen in on the app", I'd create an appropriately named null sink, connect the app to it with pavucontrol (this will be remembered by Pulseaudio), record from the monitor source of this sink (again, this will be remembered, if necessary with command line options for the recording app to set the app name for Pulseaudio). When you want to listen in, make a loopback connection from the monitor source to your loudspeaker sink. Or make this loopback permanent, and mute/unmute it as required.

You can use pacmd or pactl to try all this out on the commandline. With the same commands you can also script your shortcuts. Make it permanent by using the Pulseaudio startup scripts.

So something along the lines of

pactl load-module module-null-sink sink_name=recsink
pactl load-module module-loopback source=recsink.monitor sink=your_loadspeaker_sink

Use pactl list short sinks to see your sink names. pactl help and pacmd help for more commands.

Best Answer

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Route application’s audio output to multiple playback devices

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