Hey Arun,
Thanks for responding.
I usually point folks to the sync-playback.c test that we have a starting point, but this is certainly less than ideal.
"less than ideal" is quite the politeness. Let's see....
1) it doesn't cover files, nor does it cover files of different types (
mp3 vs wav )
Files are very good because they always work locally, which is critical
in art installations where you are being paid to deliver an experience,
regardless of whether there is connectivity. Unlike streams. Streams are
useless.
2) it doesn't cover changing sounds in response to an "interrupt", that
is, pressing a button on an art installation.
3) it doesn't cover multiple "layers", that is, different sound
experiences being added or subtracted by buttons.
Pulse audio is great all all of this, just that the example code is, to
put it your polite fashion, less than ideal, or where I come from, an
embarrassment.
The code I've written allows external REST requests, and allows the
player to make REST requests to find current state. REST being the
current lingua franca of the internet. And allows both volume changes
and source file changes. Hopefully committed literally tomorrow, putting
it through some extra tests. Will post with a permissive license.
3. If you are going to run an unattended service, you need to set
pulseaudio to be a systemd service, and you need to set up your
application as a systemd service.
In order to do this, you would typically use the 'cookie' file, which is
a binary file of undocumented type ( possibly just the contents of the
file ) which more than one process need access to. My attempts to get
this working with PulseAudio 12.0 failed, with environment variables
ignored, a service auto-creating a file with privs hard to read, but it
turns out there's a simple workaround. The documentation unhelpfully
says "maybe this is a good idea for something like an unattended
headless application but you're probably not running one of those".
The documentation is catered to users across the spectrum of use-cases and expertise, but I'm happy to incorporate suggestions for better phrasing for this.
I don't know why I struggled with cookie files for 3 days. The fact that
the created cookie file was only rw on the pulse user, and not r on the
group, slowed me down --- why shouldn't pulse group members be allowed
to use pulse audio? And what did I do wrong so that the environment
variable didn't work? I won't immediately assume a bug in pulse, but....
multiple tries..... no examples.....
-brian
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