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69 lines
1.9 KiB
Text
69 lines
1.9 KiB
Text
/** \page page_pulseaudio PulseAudio Compatibility
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# Internals - Mapping Between ALSA and Streams
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This explains the mapping between alsa cards and streams and session manager
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objects.
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## ALSA Cards
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An ALSA card is exposed as a PipeWire device.
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## Streams
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Each ALSA PCM is opened and a node is created for each PCM stream.
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# Session Manager
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## ALSA UCM
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The mapping of the PipeWire object hierarchy to the ALSA object hierarchy is the following:
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One PipeWire device is created for every ALSA card.
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- For each UCM verb, a node is created for the associated PCM devices.
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- For each UCM verb, an endpoint is created.
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In a first step: For each available combination of UCM device and modifier,
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a stream is created. Streams are marked with compatible other streams.
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Streams with the same modifier and mutually exclusive devices are grouped
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into one stream and the UCM devices are exposed on the endpoint as destinations.
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## ALSA Fallback
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Each PCM stream (node) becomes an endpoint. The endpoint references the
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ALSA device ID.
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Each endpoint has one stream (for now) called HiFi Playback / HiFi Capture.
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More streams can be created depending on the format of the node.
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## ALSA Pulse UCM
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Using the ALSA backend of PulseAudio we can create the following streams.
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## ALSA Pulse Fallback
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The pulse ALSA backend will use the mixer controls and some probing to
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create the following nodes and endpoints.
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# PulseAudio
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PulseAudio uses the session manager API to construct cards with profiles
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and sink/source with ports.
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If an endpoint references a device, a card object is created for the device.
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Each endpoint becomes a sink/source.
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Each Stream in the endpoint becomes a profile on the PulseAudio card. Because
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only one profile is selected on the device, only one stream is visible on
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the endpoint. This clashes with the notion that multiple streams can be
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active at the same time but is a PulseAudio limitation.
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Each Endpoint destination becomes a port on the sink/source.
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*/
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