An open-source, thread-safe callback workflow for synchronizing Unity events with precise moments in audio.
Unity's built-in audio system can play clips reliably, but synchronizing gameplay, animation, or visual effects to exact moments in those clips often requires one-off timing code. I built this system to bring a marker-and-callback workflow—similar to the event callbacks found in FMOD and Wwise—directly into a standard Unity project.
Designers package a clip, playback settings, and named markers inside an AudioEventAsset. An AudioEventPlayer then plays the clip and invokes each marker's UnityEvent at the correct moment. The same marker can also be found by name from code, making the workflow useful both in the Inspector and through runtime subscriptions.
The result is a lightweight, open-source layer that keeps audio timing reusable, visible, and close to the people authoring the experience.
The ScriptableObject-based AudioEventAsset is the system's source of truth. Alongside the AudioClip, it stores volume, pitch, looping, spatial blend, mixer routing, and whether callbacks should retrigger on each loop.
Each marker combines a readable name, a timestamp, and a UnityEvent. This separates the timing data from any one scene object, so the same authored audio event can be assigned to different players and wired to different gameplay responses.
The player schedules playback against AudioSettings.dspTime and checks elapsed DSP time inside OnAudioFilterRead. Because this callback runs on Unity's audio thread, it never invokes a UnityEvent or touches gameplay objects directly. Reached markers are written to a ConcurrentQueue<EventMarker> through the non-blocking Enqueue operation.
On the main thread, Update repeatedly calls TryDequeue and only then invokes each marker's UnityEvent. The queue forms a clear thread boundary: the audio thread owns precise timing detection, while the main thread owns every Unity-facing side effect. No shared list is iterated by both threads, and no lock is held inside the real-time audio callback.
Looping clips can optionally reset the marker index and retrigger their events on every pass, while one-shot playback naturally stops processing once the clip ends.
I created a custom Unity Editor window so timing can be authored by listening and looking, instead of repeatedly entering seconds by hand. It renders the selected clip's waveform, previews audio with a moving cursor, and provides zoom and horizontal navigation for precise placement.
Markers can be added directly on the waveform, dragged to a new moment, selected from the list, renamed, deleted, or fine-tuned numerically. The selected marker's UnityEvent is exposed in the same window, keeping timing and behavior together throughout iteration.
A custom AudioEventTrack, PlayableAsset, and PlayableBehaviour extend the same event system into Unity Timeline. An AudioEventPlayer can be bound to the track, allowing playback and callbacks to follow the Timeline graph alongside animation, particles, cameras, and other authored sequences.
This keeps cinematic and gameplay workflows on the same reusable AudioEventAsset model instead of requiring a second timing implementation.
