Enable short fadeout when stopping playback to prevent artifacts

[francamps]

Context

When audio playback is stopped abruptly before the clip reaches its natural endpoint, it often results in a "clicking" sound. This occurs because the audio waveform is interrupted while at a high amplitude, creating a sudden discontinuity. The occurrence of this clicking sound is unpredictable, as it depends on the random point in the waveform at which playback is halted.

This happens frequently when using the voice SDK and the user interrupts the assistant, which requires the client to stop the playback as soon as it receives the user_interruption event.

Change

This PR enables introducing a short fadeout when interrupting the assistant, which prevents any clicking sounds or other potential artifacts by stopping the playback always at a point with amplitude set to virtually 0. The fadeout can be called when clearing the buffer in the worklet. The gain manipulation is applied in the worklet itself, which allows this manipulation to occur at the sample level. The alternative of applying it via a GainNode in the main thread was discarded, as it required estimating the fadeout duration by polling the currentTime of the audio clip or using a setTimeout.

The change is backwards compatible, as it preserves the previous clear message to the worklet, which does still clear the buffer in the worklet without applying a fadeout.

Notes

This change introduces a new nomenclature to worklets: when a change to the worklet is merged, we will rename to new version as audio-worklet-YYYYMMDD.

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Name	Status	Preview	Comments	Updated (UTC)
empathic-voice-api-js-next-app	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	May 6, 2025 5:42pm

[vpicone]

Sounds great to me. Can definitely here the elimination of the audio artifact compared to main.