[LAU] Service/user not using PulseAudio

[Len Ovens]

On Wed, 8 Apr 2020, Iain Mott wrote:

> Another Asterisk PBX related question. I have the Asterisk service 
> periodically sending System commands on the host machine when particular 
> phone extensions are called. The Asterisk service is run by the user 
> asterisk. I made asterisk a member of the 'audio' group so that it can 
> use 'aplay' with the System command. eg.
>
> System(aplay -c 1 -D pulse /home/iain/sounds/line1.wav)
>
> This plays OK but plays on the laptop's internal hardware rather via 
> PulseAudio. Jack is running and is configured to use an external USB 
> sound card and the PulseAudio Jack Sink.
>
> If I run the following as user iain, it plays correctly through the USB:
>
> aplay -c 1 -D pulse /home/iain/sounds/line1.wav

two users is going to be a problem. Jack has to run as user and is not 
system. pulse can be run as a system daemon but I don't know what that 
does to a pulse->jack bridge.

Simple solution: use wires. Run the output of the onboard audio to a spare 
input on the usb device and run a spare output on the usb device to the 
onboard input.

Less simple: use networking. both pulse and jack are able to stream audio 
over the network (local host is fine) so run two instances of either jack 
or pulse and use networking to join them. I do not know pulse well 
enough to give any hints what so ever on network streaming. Jack would be 
easier. Just use netjack or zita-njbridge.

Also, ALSA has mixer plugins that may provide an extra phseudo device. I 
don't know how that works.

Contrary to popular thought, pulse does not require a display, but it does 
require access to a user dbus. Using dbuslaunch to run a screen session 
works for this. (at least this has worked for me on a headless system)

--
Len Ovens
www.ovenwerks.net