How to interpolate Tween on Audio Bus?

Question

I tried to do it in different ways but nothing comes out. My code looks like this (I know that interpolate_property method doesn't indicate what is needed at all, I showed it for clarity):

func _on_StartButton_pressed():
    fade.fade_in()

    var tween = Tween.new()
    add_child(tween)
    tween.interpolate_property(AudioStream, "volume_db", 0, -80, 1, Tween.TRANS_QUART, Tween.EASE_IN, 0)
    tween.start()

    yield(get_tree().create_timer(transition_duration), "timeout")
    get_tree().change_scene("res://Main.tscn")

I want to interpolate audiobus I need (in my case it's Music, index 1), not master audio.
Is it possible? If so, how?

Answer 1

1. You must create a method that will change the volume of your bus.
2. Use interpolate_method in your tween.

tween.interpolate_method(self, "change_audio_bus_volume", 0.0, -80.0, 1.0)
tween.start()

func change_audio_bus_volume(value: float):
    var index = AudioServer.get_bus_index("bus_name")
    AudioServer.set_bus_volume_db(index, value)

Comments

Note that this will most likely cause audible cracking as per https://github.com/godotengine/godot/issues/32882. As a workaround, modify the volume of individual AudioStreamPlayer nodes instead.