Soundtrack and animation not in sync when using autostart (for heavy scenes)

[teadrinker]

Godot version

v4.1.1.stable.mono.official [bd6af8e]

System information

Godot v4.1.1.stable.mono - Windows 10.0.19045 - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 2070 Super (NVIDIA; 31.0.15.2754) - Intel(R) Core(TM) i7-10750H CPU @ 2.60GHz (12 Threads)

Issue description

when using the autostart feature with a heavy scene, the audio is out of sync with the animation.
when calling play from a script, sync works well in the same scene.

Steps to reproduce

open project in synctest.zip and run project.
Note:

• The drums at 0s and at 16s are out of sync (using autostart)
• The drums at 32s and at 52s, sync works as expected (because script plays animation at 20s)

Minimal reproduction project

SyncTest.zip

[MJacred]

I'm not entirely sure on this, because I don't know the AnimationPlayer's code, so take this with some grain of salt: IMO, this is not a bug, but a limitation of the AnimationPlayer's autoplay on load: https://docs.godotengine.org/en/stable/classes/class_animationplayer.html#class-animationplayer-property-autoplay.

Therefore, it's triggered once the scene is loaded. This does not mean the scene is rendered. The scaling may depend on that (this is my conclusion, because waiting for the RenderingServer seems to fix it…).
Your AnimationPlayer simply triggers the audio to play. So the audio part cannot really mess up here.

In your case, this will do the trick: first, deactivate the autoplay on load for your track "new_animation". And in a script attached e.g. to your scene root node, have this code:

func _ready():
	RenderingServer.connect("frame_post_draw", play_animation)

func play_animation():
	RenderingServer.disconnect("frame_post_draw", play_animation)
	$AnimationPlayer.play("new_animation")