/**
 * Text-to-speech provider surface. fabric-harness ships ElevenLabs and
 * Cartesia implementations; bring-your-own for on-prem TTS or unsupported
 * vendors. Used by `PipelineVoiceProvider` to drive the audio-out side of
 * STT→LLM→TTS voice agents.
 *
 * For monolithic realtime models that own audio in *and* out (OpenAI
 * Realtime), use `OpenAIRealtimeVoiceProvider` directly — TTS is internal.
 */
import type { VoiceAudioFormat } from './voice.js';
export interface TtsSynthesisOptions {
    /** Voice timbre / cloned-voice id. Provider-specific. */
    voice?: string;
    /** Audio format on the wire. Default `pcm16`. */
    audioFormat?: VoiceAudioFormat;
    /** Sample rate in Hz. Default 24000 for `pcm16`, 8000 for telephony codecs. */
    sampleRate?: number;
    /** Optional speaking-rate / speed multiplier (1.0 = default). */
    speed?: number;
    /** Abort signal — terminates an in-flight synthesis cleanly. */
    signal?: AbortSignal;
}
export interface TtsSynthesisUsage {
    /** Characters of input text submitted (used for billing rollup). */
    characters: number;
    /** Total bytes of audio emitted. */
    audioBytes: number;
    /** Wall-clock duration of the synthesis call in milliseconds. */
    durationMs: number;
}
export interface TtsProvider {
    /** Stable provider id used in cost telemetry, e.g. `elevenlabs`, `cartesia`. */
    readonly name: string;
    /**
     * Synthesize a complete utterance. Yields raw audio frames in
     * `opts.audioFormat` (default `pcm16`). The final iteration value is
     * the usage rollup — read it from `provider.lastUsage()` when the
     * iterator completes.
     */
    synthesize(text: string, opts?: TtsSynthesisOptions): AsyncIterable<Uint8Array>;
    /**
     * Optional: streaming text input. The provider should chunk audio out
     * incrementally as text arrives — useful for low-latency LLM-token-to-
     * audio paths. Falls back to buffering + `synthesize()` if absent.
     */
    synthesizeStream?(text: AsyncIterable<string>, opts?: TtsSynthesisOptions): AsyncIterable<Uint8Array>;
    /** Last completed synthesis usage. Reset at the start of each call. */
    lastUsage(): TtsSynthesisUsage | undefined;
}
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