JACK: support connecting to no device (only creating ports) #932
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Previously, using the JACK backend meant that for each port:
- We call jack_port_register() to create the port,
- And call jack_connect() to create a connection between the newly
created port and a target (the parameters->device argument).
In the JACK world, it is common for processes to spawn a node with ports
and let somebody else do the routing. We therefore allow creating a
stream that targets as input and/or output paNoDevice.
This cannot be done directly using:
PaStreamParameters outputParams = {
.device = paNoDevice,
// ...
};
As with this, PortAudio cannot use the right API backend.
Instead, we do this:
PaJackStreamInfo streamInfo;
PaJack_InitializeNoDeviceStreamInfo(&streamInfo);
PaStreamParameters outputParams = {
.device = paUseHostApiSpecificDeviceSpecification,
.hostApiSpecificStreamInfo = &streamInfo,
// ...
};
streamInfo contains the standard API-specific header plus a
PaDeviceIndex device field that _must_ contain paNoDevice.
Some more details of changeset in pa_jack.c:
- Move parameter validation into an helper called from both
IsFormatSupported() and OpenStream().
- If API-specific info is provided and its device field is paNoDevice,
we create ports without calling jack_connect().
- We do not allocate stream->remote_*_ports in this case. That allows
us to detect throughout the driver without storing additional
state.
Signed-off-by: Théo Lebrun <[email protected]>
Collaborator
|
I think this is worthy of discussion, especially with people who are using JACK. |
RossBencina
added
the
src-jack
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Previously, using the JACK backend meant that for each port:
jack_port_register()to create the port,jack_connect()to create a connection between the newly created port and a target (thePaStreamParameters.deviceargument).In the JACK world, it is common for processes to spawn a node with ports and let somebody else do the routing. We therefore allow creating a stream that targets as input and/or output
paNoDevice.See the commit message for additional details.
I do have questions regarding this:
I'm not familiar with PortAudio's API so there might be something better to do. Maybe something that is generic across APIs? Wanting to create a stream without connecting to anything might not be specific to JACK.