Why is my Unity Timeline AudioTrack silent at runtime?

The most common cause is a missing AudioSource binding on the PlayableDirector. Timeline AudioTracks require a bound AudioSource component to output sound. If the binding field is empty or references a destroyed object, the track produces silence. Check the PlayableDirector's Bindings section in the Inspector.

Does Timeline audio work without an AudioSource binding?

No. Unlike the Animation Track which can animate the Director's own GameObject, the Audio Track always requires an explicit AudioSource binding. Without it, Timeline has no output device to route audio through. The clip data exists but has nowhere to play.

Why does Timeline audio play in editor but not in build?

This usually happens because the AudioClip asset is not included in the build. If the clip is only referenced through the Timeline asset and not directly by a scene object, Unity's build pipeline may strip it. Ensure the AudioClip is in a Resources folder, an Addressable group, or directly referenced by a MonoBehaviour in the scene.

Fix: Unity Timeline Audio Clip Not Playing

Quick answer: Timeline AudioTrack clips are silent when the PlayableDirector has no AudioSource bound to the track, the clip asset reference is null, the volume curve is zeroed, or a mute/solo state from the editor leaked into the asset. Check bindings first, then clip references, then curves.

Here is how to fix Unity Timeline audio clips not playing. Your cutscene plays, animations trigger correctly, but the audio track produces complete silence. The Timeline editor shows the audio waveform on the clip, scrubbing in preview mode plays audio fine, but at runtime — nothing. The AudioClip is assigned, the track is not muted in the editor, and yet the game is silent where it should not be.

The Symptom

A PlayableDirector plays a Timeline asset that contains one or more Audio Tracks. In the editor preview (scrubbing the timeline), audio plays correctly. When you enter Play mode or run a build, the audio track is completely silent while all other tracks (Animation, Activation, Signal) work normally.

No errors appear in the console. The PlayableDirector state shows Playing. The Timeline is clearly running because other tracks execute their clips on schedule.

What Causes This

Missing AudioSource binding. Every Audio Track in a Timeline requires a bound AudioSource component. The PlayableDirector’s bindings panel maps each track to a scene object. If the Audio Track binding is None, audio has no output target. The editor preview bypasses this by using an internal preview AudioSource, which is why scrubbing works but runtime does not.

Null clip asset reference. If the AudioPlayableAsset on the clip lost its reference to the AudioClip file (due to a moved or deleted asset), the clip plays silence. The waveform preview may still show from cached data even though the actual reference is broken.

Volume curve set to zero. Each audio clip in Timeline has a volume curve property. If this curve was accidentally set to a constant value of 0 (or an animation curve that evaluates to 0 at the current time), the audio plays at zero volume.

Mute or solo state persisted. The Timeline editor has Mute (M) and Solo (S) buttons per track. These states are serialized into the Timeline asset. If you muted a track during editing and forgot to unmute it, the track stays muted at runtime.

The Fix

Step 1: Bind an AudioSource to the track. Select the GameObject with the PlayableDirector. In the Inspector under Bindings, find the Audio Track entry. Assign an AudioSource component from the scene.

// Bind AudioSource via script if setting up at runtime
var director = GetComponent<PlayableDirector>();
var timeline = director.playableAsset as TimelineAsset;

foreach (var track in timeline.GetOutputTracks())
{
    if (track is AudioTrack audioTrack)
    {
        director.SetGenericBinding(audioTrack, audioSource);
    }
}

Step 2: Verify clip asset references. Click each audio clip in the Timeline. In the Inspector, check that the AudioPlayableAsset has a valid Clip field pointing to an actual AudioClip asset. If it says “Missing” or “None,” re-assign the audio file.

Step 3: Check the volume curve. Select the audio clip in Timeline. In the Inspector, expand the clip properties. The volume property should show a curve or a constant value of 1. If it is 0, reset it.

// Debug: log all audio clip volumes in a timeline
foreach (var track in timeline.GetOutputTracks())
{
    if (track is AudioTrack audioTrack)
    {
        foreach (var clip in audioTrack.GetClips())
        {
            var asset = clip.asset as AudioPlayableAsset;
            Debug.Log($"{clip.displayName}: clip={asset.clip}, vol curve keys={clip.curves}");
        }
    }
}

Step 4: Unmute the track. Open the Timeline window, look for the M (mute) icon on the audio track. If it is highlighted, click it to unmute. Also check that no other track has Solo (S) enabled, as Solo mutes all non-soloed tracks.

Build-Specific Issues

If audio works in the editor but not in a build, verify the AudioClip is actually included. Timeline assets reference clips indirectly through AudioPlayableAsset sub-assets. If the clip is not otherwise referenced by any scene object and is not in a Resources or Addressables group, the build system may exclude it. Add the clip to a Resources folder or create an explicit reference in a MonoBehaviour.

“Timeline preview lies to you — it uses its own AudioSource. Runtime requires you to provide one.”

Common Gotcha: Spatial Blend

If the bound AudioSource has Spatial Blend set to 1 (fully 3D) and the AudioSource is far from the Audio Listener, the audio plays but is inaudible due to distance attenuation. Set Spatial Blend to 0 for non-positional Timeline audio like music or voiceover.

Nine times out of ten it is a missing binding. The editor preview hides this from you because it creates its own temporary AudioSource.