/**
 * OpenAI speech services: TTS (text-to-speech) and Whisper transcription.
 *
 * Extracted from openai.ts for modular decomposition (Phase 3B).
 */
/** Valid TTS voice names. */
export declare const TTS_VOICES: readonly ["alloy", "echo", "fable", "onyx", "nova", "shimmer"];
export type TTSVoice = (typeof TTS_VOICES)[number];
/**
 * Convert text to speech using OpenAI TTS API.
 * Returns OGG Opus audio suitable for Telegram's sendVoice.
 */
export declare function textToSpeech(text: string, apiKey: string, voice?: TTSVoice): Promise<Buffer>;
/**
 * Transcribe an audio buffer using an OpenAI-compatible Whisper endpoint.
 *
 * Provider is swappable via env vars (all optional, default to OpenAI):
 *   TRANSCRIPTION_BASE_URL  e.g. https://api.groq.com/openai/v1
 *   TRANSCRIPTION_API_KEY   provider key (falls back to the passed key)
 *   TRANSCRIPTION_MODEL     e.g. whisper-large-v3 (default: whisper-1)
 *
 * @param audioBuffer  Raw audio content (OGG Opus from Telegram voice messages).
 * @param apiKey       Fallback API key (used when TRANSCRIPTION_API_KEY is unset).
 * @param filename     Upload filename (extension drives Whisper's format sniffing).
 * @param audioSeconds Clip duration, when known — used for cost metering only.
 * @param threadId     Originating thread, when known — used for usage attribution only.
 * @returns The transcribed text (empty string if no speech detected).
 */
export declare function transcribeAudio(audioBuffer: Buffer, apiKey: string, filename?: string, audioSeconds?: number, threadId?: number): Promise<string>;
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