[pulseaudio-discuss] need to run `pulseaudio -k` to record from null sink

[Sean Greenslade]

On Tue, Sep 07, 2021 at 08:18:48AM +0100, Gareth Walker wrote:
> On Tue, 7 Sept 2021 at 00:12, Sean Greenslade <sean at seangreenslade.com>
> wrote:
> 
> > Can you look at the logs to see if there are any errors listed when you
> > load the modules. The logs should be in your user journal, try this:
> >
> > $ journalctl --user -u pulseaudio.service -e
> >
> 
> Thanks for the tip. This is what appears in the user journal after reboot:
> 
> systemd[1679]: Starting Sound Service...
> pulseaudio[1685]: No such source.

OK, so the above line confirms my theory. The loopback module is loaded
too soon, and the automatic loader hasn't had time to load in the alsa
soundcards yet.

> <snip rest of logs>

I've run into this myself, and I can't really think of any great
workarounds to handle this entirely within pulse. If your alsa
identifiers are suitably stable, you could maybe manually load the
module-alsa-* modules before the loopback, but that seems fragile,
especially with USB devices.

What would be ideal is if there were an option for module-loopback to
treat the source= and sink= options as soft-preferences, automatically
switching to them when they become available. While I can't commit to
writing a patch right now, it looks reasonably straightforward. Pulse
devs, would you be open to accepting such a patch? Or do you see a more
straightforward way of accomplishing this task?

--Sean