[pulseaudio-discuss] PulseAudio, switch audio output on device connection

[Mark Gaiser]

On Sun, Oct 26, 2014 at 6:18 PM, Tanu Kaskinen
<tanu.kaskinen at linux.intel.com> wrote:
> On Sun, 2014-10-19 at 13:20 +0200, Mark Gaiser wrote:
>> On Sun, Oct 19, 2014 at 12:01 PM, Tanu Kaskinen
>> <tanu.kaskinen at linux.intel.com> wrote:
>> > On Thu, 2014-10-09 at 00:39 +0200, Mark Gaiser wrote:
>> >> Note the hdmi sink is now suddenly playing the sound!
>> >> I would expect the sink to continue device that was sitting idle, but
>> >> somehow it picked the other device.
>> >> Did i actually find a bug just now or is this also some magic setting
>> >> that i can change somewhere?
>> >
>> > It's a bug (or an unimplemented feature, depending on your point of
>> > view). I didn't try to reproduce this, but I speculate that this
>> > happens, because at the time when module-rescue-streams notices that the
>> > headset is going away, it would like to move the stream to the default
>> > sink, but at that time the default sink is still the headset, so instead
>> > of the default sink, module-rescue-streams uses some other heuristics
>> > for choosing the sink where it moves the stream. When the headset
>> > finally disappears, the analog sink becomes the new default, based on
>> > different heuristics than what module-rescue-streams used.
>> >
>> > When you re-attach the usb headset, the move doesn't happen, because the
>> > stream is not connected to the default sink, and
>> > module-switch-on-connect only moves streams that are connected to the
>> > default sink.
>> >
>> > While better automatic routing is very much in my interests, it's not
>> > the highest priority right now, so I don't know when this will be fixed.
>> > There was some talk last week about improving module-device-manager and
>> > then enabling it by default. If someone is going to work on that, it
>> > will quite likely fix this issue.
>> >
>> > As a workaround, you can set the HDMI card profile to "off".
>>
>> Hi Tanu,
>>
>> Thank you very much for the detailed description. To me it sounds like
>> module-rescue-streams might have a bug then. Also,
>> module-rescue-streams apparently moves the stream to my hdmi, but
>> shouldn't that become the default then? I mean, that would make
>> module-switch-on-connect work again on re-attaching cases.
>
> I think we should refactor things so that module-rescue-streams would
> use the same code for figuring out the target sink as what is used when
> the new default sink is decided. I created a formal bug report:
> https://bugs.freedesktop.org/show_bug.cgi?id=85488

Thank you very much for that.
>
>> Or another way; Shouldn't module-rescue-streams only be invoked when a
>> device actually disappeared? I mean, that would probably fix the
>> stream moving back to the default stream and would also fix the
>> re-attach case, right?
>
> When the device actually disappears, streams connected to it get killed.
> That's why module-rescue-streams has to act before the device actually
> disappears.

Oke, sounds sane to me. But there must be some code somewhere in
pulseaudio that lets a stream kill gracefully, right? For instance in
some desctructor (if it where C++.. it's C but you probably get the
idea). That "destructor" could be used to gracefully move the
(otherwise killed) stream to a new default.

It's just an idea.