Re: Switching output sink(?)

[Mike Kazantsev]

On Fri, 30 Oct 2020 22:01:43 +0530
Mandar Mitra <mandar.mitra@gmail.com> wrote:

> I can use the mate volume control applet to switch between the
> builtin speakers on my computer and an external speaker connected via
> bluetooth.
> Other applications like Firefox and mpv (played from the command-line)
> send the output to whatever is currently selected as the sound sink,

With mpv this should probably happens when you start a fresh instance,
so it selects new default sink, but if you start mpv before switching,
it won't auto-migrate running playback stream to a new sink, correct?


> but emms seems to always send output to the default builtin speaker,
> even when a bluetooth speaker is connected and selected in the volume
> control applet.

If you use mpv as a player in emms, then it should use a long-running
mpv process that doesn't get restarted between tracks by default.

It does however close and re-open the output stream for each track,
which might play on the new default sink, so that might be a hacky fix,
if the issue is only with currently-playing stuff - hit "stop" and then
"play" key.
Not a nice fix though, obviously.

(not entirely sure if mpv/libpulse will use different sink for new
stream, but it probably should, unless directed to do otherwise via
e.g. PULSE_SINK env option)


> I can probably use the discussion here
> 
> https://askubuntu.com/questions/71863/how-to-change-pulseaudio-sink-with-pacmd-s
> et-default-sink-during-playback
> 
> and cobble together an elisp function to run the necessary shell commands, but
> don't know how to integrate this into emms.

To be clear, one of the essential commands that you're talking about is
something like "pactl move-sink-input 5 1"?
I.e. to move currently-playing music stream to a new sink?

As I assume that you change default sink in the desktop environment
applet already (as otherwise not sure what else it might be doing),
so there's no need to run that part from the link.


> Could you please give me a hint or two -- maybe point me to which .el files I
> should look at for more info? Or let me know that this is not easily doable?

Do you want emacs or emms to detect when default sink in pulseaudio
changes and migrate running mpv playback stream to a new default sink?

Don't think it has much to do with emms, as it doesn't monitor
pulseaudio state in any way, and doesn't really know that it even
exists, as only mpv interacts with it, if it is the output configured
there.

I'd suggest these options:

- Checking DE volume applet for some hook that it might run when
  changing sinks and adding a script there to also migrate any running
  streams.

- Contacting applet devs, asking if there's an option to do that, and
  maybe considering adding it, as it sounds generally useful.

- Making a script that'd do that independently of emms (as again, it
  shouldn't have much to do with this).

  For example, with shell, guess you can monitor "pactl subscribe"
  output and react to relevant sink state changes there.
  Or you can make same script with e.g. python, elisp or in any other
  language, of course, some of which have more convenient libpulse
  bindings.

But feel like maybe I've misunderstood the question, given how it seem
to be directed to this mailing list, while having little to do with
emms in my current understanding.


-- 
Mike Kazantsev // fraggod.net