audioLevel / mic monitoring not available during previewOnly (lobby) mode

[czoli1976]

Context

The previewOnly prop on OTPublisher (feature request #222) renders the local camera before publishing, enabling a waiting-room / lobby experience. A common lobby need is a mic level indicator — showing the user their microphone works before they join.

Limitation

The native Android and iOS Vonage Video SDKs only begin audio capture when the publisher is published. In previewOnly mode the publisher is intentionally not published, so audioLevel events are never emitted — the React Native wrapper has no audio level to forward during preview.

Repro: mount <OTPublisher previewOnly /> with an audioLevel handler → no audioLevel events fire until previewOnly is set to false (the publisher publishes).

Why this isn't solved in the wrapper

Working around it at the RN layer would mean opening an independent microphone capture (an AVAudioEngine tap on iOS / AudioRecord on Android) alongside the SDK. That double-opens the mic, fights the SDK's own capture lifecycle, and risks audio-route/echo issues — so it shouldn't be done in the wrapper.

Suggested direction

• Short term (done): documented in the previewOnly README — audioLevel is unavailable during preview.
• Proper fix: the native Video SDKs need to expose a preview-time audio level (or a standalone mic-level API) that the RN wrapper can forward while previewOnly is active. This should be raised with the native Android/iOS SDK team.

Tracking this alongside the previewOnly feature (#222).

[czoli1976]

Update — re-confirmed on the 2.35.0 native SDK RC (both platforms)

Re-tested the previewOnly lobby on the upcoming 2.35.0 native SDK RC (Android build 1220 / iOS build 1215), on-device:

Phase	audioLevel events
Standalone preview (previewOnly=true, no session)	0
In-session lobby (previewOnly=true, connected)	0
After publish (previewOnly=false)	72 (iOS) / 126+ (Android)

This is structural, not a wiring gap on the RN side. Our wrapper attaches the publisher audioLevel listener/delegate during preview on both platforms, yet it receives nothing until publish. The publisher's audioLevel reflects the audio actually being sent to the session — so there is simply no level to report until the publisher is publishing.

Because the value is tied to the publish path, there is no JS/wrapper workaround: surfacing a mic-level meter in the lobby would require the native SDK to expose a capture-side level that is independent of an active publish. Confirmed absent in both the shipping 2.34.1 and the 2.35.0 RC.

Implemented alongside #226 (previewOnly).