ADR 0001 Audio Routing

ADR 0001 — Audio routing (TTS playback sink)

Status: Accepted
Date: 2026-08-02
Milestone: M0.6

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Context

CONTRACTS §6 asked whether TTS audio should play in:

• (a) the kiosk (Chromium), keeping lip-sync on one clock, or
• (b) the audio process via ALSA, lower latency but separate timing to the avatar.

The Pi has HDMI + headphones sinks and a working Chromium/labwc session. TalkingHead (when used) requires audio + visemes aligned in the browser for reliable lip-sync.

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Decision

Choose (a) — kiosk is the audio sink.

• Bridge sends speak with audioUrl (loopback HTTP) to the kiosk.
• Kiosk plays audio and emits speak.started / speak.ended.
• Follow-up window opens on speak.ended from the kiosk.
• Bridge → audio play message is not used in Phase 1.

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Consequences

• Accept ~100 ms extra latency vs raw ALSA for guaranteed sync.
• If Chromium audio on the Pi proves unreliable in M7 UAT, revisit and write a superseding ADR.
• CONTRACTS §2 play remains documented as unused/reserved.

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Related

• Contracts — Bridge ↔ Kiosk
• Kiosk & Avatar
• ADR Index