Bug Character offset issue when Timeline GameObject is not selected (100% reproducible)

Hello, I'm running into a very weird bug where a character position is being offset during an animation blend. It's as if both animations positions are being added instead of blended. This only happens before selecting the Timeline GameObject for the first time, after play starts.
Important to note that I'm creating the track and adding the clips to it at runtime.

Here's a video of the issue:

And here's the code that reproduces the issue:

Code (csharp):

1.  
2. using UnityEngine;
3. using UnityEngine.Playables;
4. using UnityEngine.Timeline;
5.  
6. public class TimelineTest : MonoBehaviour
7. {
8.     [SerializeField] private PlayableDirector _playableDirector;
9.     [SerializeField] private Animator _animator;
10.     [SerializeField] private AnimationClip _animationClip1;
11.     [SerializeField] private AnimationClip _animationClip2;
12.  
13.     private TimelineAsset _timelineAsset;
14.     private AnimationTrack _animationTrack;
15.  
16.     private void Start()
17.     {
18.         // Create TimelineAsset
19.         _timelineAsset = ScriptableObject.CreateInstance<TimelineAsset>();
20.         _playableDirector.playableAsset = _timelineAsset;
21.  
22.         // Create AnimationTrack and add it to the timeline
23.         _animationTrack = _timelineAsset.CreateTrack<AnimationTrack>(null, "Animation Track");
24.         _animationTrack.trackOffset = TrackOffset.ApplySceneOffsets;
25.  
26.         // Bind the animation track to the animator
27.         _playableDirector.SetGenericBinding(_animationTrack, _animator);
28.  
29.         // Create animation clip 1
30.         var timelineClip = _animationTrack.CreateClip(_animationClip1);
31.         timelineClip.start = 1;
32.  
33.         // Create animation clip 2
34.         timelineClip = _animationTrack.CreateClip(_animationClip2);
35.         timelineClip.start = 4f;
36.  
37.         // Rebuild graph and play
38.         _playableDirector.RebuildGraph();
39.         _playableDirector.Play();
40.     }
41. }
42.  

And here's the repro project with the code you see above: https://www.icloud.com/iclouddrive/03dboZpFKXEqVI0DZtVbaxAkg#TimelineTest

Any help would be greatly appreciated!

P.S.: Forgot to mention that this happens on every Unity version I tested (2021, 2022 and 2023) and Timeline version as well (1.4 up to 1.8.2)

 

I'm not sure if this is the reason, but

CreateClip()

won't set the

TimelineClip.blendInDuration / blendOutDuration

for you, so you have to calculate the overlap time and set the blend time by yourself.
(The Timeline Editor friendly updates that for you, so you would start get proper blending when you first open the Editor)

 

Thanks @Yuchen_Chang and @julienb! That fixed it!

I couldn't find this information anywhere in the documentation and with the Editor behaviour shown in my recording, it really made it look like a bug.