Assistance with editing links via WirePlumber

[Louis DeLosSantos]

Thanks a lot.

On Fri, Feb 9, 2024 at 9:00 AM George Kiagiadakis <mail at gkiagia.gr> wrote:

> Yes, you can use the metadata object without the PA API.
>
>
>
> On 8 Feb 2024, at 20:01, Louis DeLosSantos <louis.delos at gmail.com> wrote:
>
> Thanks a ton for the info.
>
> I dug at this for awhile and yes, I wound up just calling into the pulse
> audio api to switch sink inputs.
>
> I dug enough to find that this file:
>
> https://gitlab.freedesktop.org/pipewire/pipewire/-/blob/master/src/modules/module-protocol-pulse/modules/module-stream-restore.c?ref_type=heads
>
> Is writing to metadata. I kinda quit there, because I couldnt tell if the
> metadata it was writing was "stuck" in the pulse audio module or was made
> available to the pipewire api proper.
>
> Sounds like from your response that the state that the pa stream restore
> module stashes on metadata is indeed available at the "default-metadata"
> object that I can retrieve on the registry?
>
> If so, thats great, i can remove the call into pulse-audio library and
> just use wireplumber/pipewire.
>
> On Thu, Feb 8, 2024 at 3:46 PM George Kiagiadakis <mail at gkiagia.gr> wrote:
>
>> Hi,
>>
>> Yes, it is easy to re-link streams to different sinks, similar to
>> pavucontrol.
>>
>> You can do this by setting the “target.object” property in the “default”
>> metadata object. The value may be the “node.name" or the “object.serial”
>> of the target sink/source that you want to link your stream with.
>>
>> On the command line:
>>
>> pw-metadata -n default <ID of the stream> “target.object” “<name of the
>> sink>” “Spa:String"
>>
>> For example:
>>
>> pw-metadata -n default 45 “target.object”
>> “alsa_output.pci-0000_00_1f.3.analog-stereo” “Spa:String"
>>
>> Using the WirePlumber C API, you need to find the WpMetadata object
>> first, using an object manager (use a constraint on “metadata.name” to
>> match “default”) and then set the value with:
>>
>> wp_metadata_set (metadata, stream_node_id, PW_KEY_TARGET_OBJECT,
>> “Spa:String”, target_node_name);
>>
>> PS: If you set the “object.serial” instead of the name, then the type
>> should be “Spa:Id” instead.
>>
>> This is the same mechanism that is used by existing tools like
>> pavucontrol. You can also use pavucontrol to see this in action. Use
>> “pw-metadata -n default” to print the existing metadata values for
>> inspection.
>>
>> I hope this helps.
>>
>> Best regards,
>> George
>>
>>
>> > On 26 Jan 2024, at 18:09, Louis DeLosSantos <louis.delos at gmail.com>
>> wrote:
>> >
>> > Hey all,
>> >
>> > I'm writing a Linux desktop shell which will have a built in audio
>> mixer.
>> > I'm trying to isolate the API usage to the WirePlumber C API.
>> >
>> > Is it currently possible to "re-link" input or output streams to a
>> > different sink/source via WirePlumber?
>> >
>> > Is anyone able to point me to examples of doing this? I'm a bit
>> > confused about whether I need to delete the existing link and create a
>> > new one, or if I can update the existing link with new input/output
>> > ports.
>> >
>> > Thanks a lot.
>>
>>
>
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