add preconnect audio buffer API to LocalAudioTrack

[theomonnom]

No description provided.

[devin-ai-integration]

Devin Review found 1 potential issue.

View 3 additional findings in Devin Review.

[devin-ai-integration]

🔴 Registering async callback with EventEmitter.on() always raises ValueError

The _setup_preconnect_auto_send method defines _on_participant_active as an async def and registers it with room.on("participant_active", _on_participant_active) at line 816. However, EventEmitter.on() (event_emitter.py:160-163) explicitly rejects async callbacks by raising ValueError("Cannot register an async callback with .on(). Use asyncio.create_task within your synchronous callback instead."). This means the auto-send feature will always crash with a ValueError when _setup_preconnect_auto_send is called, which propagates up through publish_track() when preconnect_buffer_auto_send_to is set and the track has a preconnect buffer.

Prompt for agents

The _setup_preconnect_auto_send method in participant.py defines _on_participant_active as an async function and tries to register it with room.on("participant_active", ...) at line 816. However, EventEmitter.on() (in event_emitter.py:160-163) raises ValueError when given an async callback.

The fix should follow the pattern recommended by the error message: define a synchronous callback that internally creates a task. For example:

def _on_participant_active(participant: RemoteParticipant) -> None:
    if participant.identity != target_identity:
        return
    if not track.has_preconnect_buffer:
        return
    room.off("participant_active", _on_participant_active)
    asyncio.ensure_future(_send_preconnect(participant))

async def _send_preconnect(participant: RemoteParticipant) -> None:
    try:
        await track.send_preconnect_buffer(destination_identity=participant.identity)
    except Exception:
        logger.exception("failed to auto-send preconnect buffer")

room.on("participant_active", _on_participant_active)

This is in _setup_preconnect_auto_send in livekit-rtc/livekit/rtc/participant.py. The EventEmitter.on() constraint is in livekit-rtc/livekit/rtc/event_emitter.py:159-163.

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