/**
 * Audio Compression Utilities
 */
export interface CompressionResult {
    buffer: Buffer;
    format: string;
}
/** When TTS returns WAV, ffmpeg can target Opus (Telegram, etc.) or MP3 (Weixin VoiceItem, webchat). */
export type WavCompressionTarget = 'opus' | 'mp3';
/**
 * Compress WAV using ffmpeg. Non-WAV inputs are returned unchanged.
 * Default `wavTarget` is Opus (common for Telegram voice).
 */
export declare function compressAudio(audioBuffer: Buffer, inputFormat: string, wavTarget?: WavCompressionTarget): Promise<CompressionResult>;