script.lua

local function create_null_sink()
  print("Creating null sink")

  null_node = Node("adapter", {
    ["factory.name"] = "support.null-audio-sink",
    ["media.class"] = "Audio/Sink",
    ["object.linger"] = true,
    ["audio.position"] = "[FL FR]",
    ["node.name"] = "automatic-null-sink",
  })

  null_node:activate(Feature.Proxy.BOUND)
end

om = ObjectManager {
  Interest { type = "node",
    Constraint { "media.class", "matches", "Audio/*" },
    Constraint { "node.name", "not-equals", "automatic-null-sink" },
  },
}

om:connect("object-added", function(om, node)
  print("Node added:", node)
  Debug.dump_table(node.properties)

  if null_node and om:get_n_objects() >= 1 then
    print("Destroying null sink")

    null_node:request_destroy()
    null_node = nil
  end
end)

om:connect("object-removed", function(om, node)
  print("Node removed:", node)
  Debug.dump_table(node.properties)

  if not null_node and om:get_n_objects() == 0 then
    create_null_sink()
  end
end)

om:connect("installed", function(om)
  print("Installed object manager")

  if om:get_n_objects() == 0 then
    create_null_sink()
  end
end)

om:activate()