BabylonJS/Babylon.js · error · Error

Connect failed

Error message

Connect failed

What it means

AudioBus.outBus setter throws "Connect failed" when, after detaching any previous bus, it subscribes to the new bus's dispose observable and _connect(this._outBus) returns false. Same family as error 35 but on the AudioBus class: chaining buses fails because the audio engine cannot connect the bus's node to the target bus's node.

Source

Thrown at packages/dev/core/src/AudioV2/abstractAudio/audioBus.ts:73

        if (this._outBus === outBus) {
            return;
        }

        if (this._outBus) {
            this._outBus.onDisposeObservable.removeCallback(this._onOutBusDisposed);

            if (!this._disconnect(this._outBus)) {
                throw new Error("Disconnect failed");
            }
        }

        this._outBus = outBus;

        if (this._outBus) {
            this._outBus.onDisposeObservable.add(this._onOutBusDisposed);

            if (!this._connect(this._outBus)) {
                throw new Error("Connect failed");
            }
        }
    }

    /**
     * The spatial audio features.
     */
    public get spatial(): AbstractSpatialAudio {
        if (this._spatial) {
            return this._spatial;
        }
        return this._initSpatialProperty();
    }

    /**
     * The stereo features of the audio bus.
     */
    public abstract readonly stereo: AbstractStereoAudio;

View on GitHub (pinned to 0592b347b8)

Solutions

1. Await AudioEngineV2 init/start before wiring bus-to-bus connections.
2. Verify the target bus belongs to the same engine instance and is not disposed.
3. Create buses via the engine API after engine readiness and keep live references.
4. Retry the assignment in try/catch once the engine reports ready.

Example fix

// before
const sfx = new AudioBus("SFX");
sfx.outBus = mainBus; // engine not ready -> Connect failed

// after
await engine.initAsync();
const sfx = new AudioBus("SFX");
sfx.outBus = mainBus;

function canWireBusToBus(engine, target) {
  return engine.state === 'started' && !!target && !target.isDisposed && engine.buses.includes(target);
}
if (canWireBusToBus(audioEngine, mainBus)) sfxBus.outBus = mainBus;

function isEngineOwnedBus(x, engine) {
  return x instanceof AudioBus && engine.buses.includes(x) && !x.isDisposed;
}

try {
  sfxBus.outBus = mainBus;
} catch (e) {
  if (e.message === 'Connect failed') {
    await audioEngine.initAsync();
    sfxBus.outBus = mainBus;
  } else throw e;
}

When it happens

Trigger: Assigning audioBus.outBus to a disposed bus, to a bus not yet added/created on a started engine, or calling the setter before the AudioEngine V2 is initialized/started.

Common situations: Building nested bus graphs (SFX -> music bus -> main output) at startup before awaiting engine readiness; passing a bus from a different engine instance; typo leading to an undefined/disposed bus reference.

Related errors

• Connect failed
• Disconnect failed
• The value passed to [Scene.audioListenerPositionProvider] mu
• The value passed to [Scene.audioListenerRotationProvider] mu
• Disconnect failed

AI-assisted analysis of BabylonJS/Babylon.js@0592b347b8 (2026-08-30). Data as JSON: /api/errors/464c3bf19e24ea25. Report an issue: GitHub.