Linking Scripts

These scripts contain all the logic for creating links between nodes. This involves, to a large extent, deciding which links to create.

Hooks

The hooks in this section are organized in 3 sub-categories. The first category includes hooks that are triggered by changes in the graph. Some of them are tasked to schedule a "rescan-for-linking" event, which is the lowest priority linking event and its purpose is to scan through all the linkable session items and link them to a particular target. The "rescan-for-linking" event is always scheduled to run once for all the graph changes in a cycle. This is achieved by flagging the event as already scheduled in the module-standard-event-source; this flag is then cleared by a hook that runs on this event.

Selecting a target for each linkable and linking to it is deferred to another set of hooks by pushing a "select-target" event for each linkable. This event is the highest priority event and therefore no other changes in the graph are processed while targets are being selected.

Hooks triggered by changes in the graph

Hook name	File	Triggered by	Action
linking/rescan-trigger	rescan.lua	linkable SI added|removed or metadata-changed	schedules rescan-for-linking event
linking/linkable-removed	rescan.lua	linkable SI removed	destroys links related to the removed linkable
linking/rescan-trigger-on-linkable-added-removed	rescan-on-linkable.lua	linkable SI added|removed	schedules rescan-for-linking; can be disabled by setting hooks.linking.rescan-on-linkable = disabled in wireplumber.profiles
linking/rescan-trigger-on-target-metadata-changed	rescan.lua	metadata-changed on target.object or target.node	schedules rescan-for-linking when node target metadata properties are changed; registered only while the linking.allow-moving-streams setting is enabled
linking/linkable-added-immediate	rescan.lua	linkable SI added	links the new linkable immediately, without waiting for a full rescan, when it is a simple stream node
linking/session-item-added	rescan.lua	session-item-added	re-enables rescanning (see linking/bluez-session-item-removed)
linking/bluez-session-item-removed	rescan.lua	session-item-removed on a bluez5 device	disables rescanning for 2 seconds, to avoid audio being played on internal nodes while the BT device switches profiles
linking/rescan-media-role-links	rescan-media-role-links.lua	link SI added, removed or metadata-changed	activates or deactivates role-based links based on role priorities and actions
linking/mpris-pause@track-links	mpris-pause.lua	link added|removed	tracks which MPRIS media players are linked to which sinks
linking/mpris-pause	mpris-pause.lua	session-item-removed on an input device linkable	pauses the MPRIS media applications whose streams were linked to the sink that is going away

Note

The linking/mpris-pause* hooks are only registered while the linking.pause-playback setting is enabled.

rescan-for-linking hooks, in order of execution

Hook name	File	Description
m-standard-event-source/rescan-done	module-standard-event-source.c	clears the rescan_scheduled flag
linking/mpris-pause-disable-rescan	mpris-pause.lua	stops the rescan while MPRIS media players are still being paused, and re-schedules it afterwards; only registered while linking.pause-playback is enabled
linking/rescan	rescan.lua	schedules select-target for each linkable session item

select-target hooks, in order of execution

Hook name	File	Description
linking/find-defined-target	find-defined-target.lua	Select the target that has been defined explicitly by the 'target.object' property or metadata
linking/find-audio-group-target	find-audio-group-target.lua	Select the audio group loopback node as target, if the subject belongs to an audio group
linking/find-filter-target	find-filter-target.lua	Select the target of a filter node, if the subject is a filter node
linking/find-media-role-target	find-media-role-target.lua	Select the target based on the stream's media.role and the target's device.intended-roles
linking/find-media-role-sink-target	find-media-role-sink-target.lua	Pick up the preferred target node for the output stream of a role-based loopback
linking/find-default-target	find-default-target.lua	Select the default source/sink as target
linking/find-best-target	find-best-target.lua	Select target based on priority.session
linking/get-filter-from-target	get-filter-from-target.lua	Translate the found target to a filter target that should be linked instead
linking/prepare-link	prepare-link.lua	Break existing link if needed, check if the target is available for linking; send error to the client if needed
linking/link-target	link-target.lua	Create si-standard-link session item to create links between the subject linkable and the selected target

Extending target selection

The select-target hooks above form a chain: each one bypasses itself if a target has already been picked, so the first hook that finds a target wins. A custom script can therefore participate in target selection simply by registering another hook on the select-target event and ordering it relative to the stock hooks with before / after.

Example 4: participating in target selection walks through such a hook in full: the script itself, the wireplumber.conf.d fragment that defines a component for it and enables it in the main profile, and the reasoning behind the ordering key and the bypass guard.