Default Nodes Scripts

These scripts contain logic to select default source and sink nodes and also manage user preferences regarding those.

Hooks

Management of the default source and sink nodes is implemented by scanning all the available nodes in the graph and assigning them a priority based on certain logic. The node with the highest priority in each category becomes the default.

Scanning is implemented using a “rescan-for-default-nodes” event. The “default-nodes/rescan-trigger” hook is the one that monitors graph changes and schedules “rescan-for-default-nodes”. Then, the “default-nodes/rescan” hook is executed for the “rescan-for-default-nodes” event and it pushes a “select-default-node” event for each one of the categories where a default node is required:

• Audio sink

• Audio source

• Video source

Hooks triggered by changes in the graph

Hook name	File	Triggered by	Action
default-nodes/rescan-trigger	rescan.lua	linkables added/removed or default.configured.* metadata changed	schedule rescan-for-default-nodes
default-nodes/store-configured-default-nodes	state-default-nodes.lua	default.configured.* metadata changed	stores user selections in the state file
default-nodes/metadata-added	state-default-nodes.lua	metadata object created	restores default.configured.* values from the state file

Hooks for the rescan-for-default-nodes event, in order of execution

Hook name	File	Description
m-standard-event-source/rescan-done	module-standard-event-source.c	clears the rescan_scheduled flag
default-nodes/rescan	rescan.lua	schedules select-default-node for each category

Hooks for the select-default-node event, in order of execution

Hook name	File	Description
default-nodes/find-best-default-node	find-best-default-node.lua	prioritizes nodes based on their priority.session property
default-nodes/find-selected-default-node	find-selected-default-node.lua	prioritizes the current default.configured.* node, i.e. the current user selection
default-nodes/find-stored-default-node	state-default-nodes.lua	prioritizes past user selections from the state file
default-nodes/apply-default-node	apply-default-node.lua	sets the highest priority selected node as the default in the metadata

Note

The actual order of the “default-nodes/find-*” hooks is not defined and doesn’t matter. The only thing that matters is that “default-nodes/apply-default-node” is the last hook.

select-default-node event

High priority event to select the default node for a given category (media.type & direction combination).

In this event, each hook is tasked to find the highest priority node of the category it runs for. In order to do that, a list of available nodes is calculated in advance, by the “default-nodes/rescan” hook, and passed on to each of the “select-default-node” hooks via event data. Each hook then has to go through this list and select a node, placing it in the “selected-node” event data together with its priority number in “selected-node-priority”. The next hook, then, may override the “selected-node” and “selected-node-priority” with something else, but only if the new priority is higher than the old one.

Event properties

Property name	Description
default-node.type	the suffix of the metadata keys related to this default node (audio.sink, audio.source or video.source)

Exchanged event data

Name	Description
available-nodes	JSON array of all selectable nodes, with each element containing all node properties
selected-node	the selected node’s node.name (string)
selected-node-priority	the priority (integer)