export interface DuckingOptions {
    /**
     * Sidechain threshold (linear amplitude, 0-1). When the voice exceeds
     * this, the compressor clamps the music. Default 0.02 — matches typical
     * dialogue average energy. Real-world podcast implementations cluster at
     * 0.012–0.03; below 0.02 even quiet voice triggers ducking, above 0.05
     * quiet conversation won't duck the music at all.
     */
    threshold?: number;
    /** Compression ratio. Default 8. */
    ratio?: number;
    /** Attack time in ms. Default 5. */
    attackMs?: number;
    /** Release time in ms. Default 250. */
    releaseMs?: number;
    /** Voice gain in linear amplitude. Default 1 (unchanged). */
    voiceGain?: number;
    /** Background gain (post-duck) in linear amplitude. Default 1. */
    bgGain?: number;
    signal?: AbortSignal;
}
export interface DuckingResult {
    output: string;
    filterGraph: string;
}
/**
 * Render a voice + background mix with the background ducked underneath the
 * voice. Both inputs may be audio or video files; the output is whatever
 * extension you give it (PCM .wav for max quality, .m4a/.aac for size).
 */
export declare function duckAudio(voicePath: string, bgPath: string, outputPath: string, opts?: DuckingOptions): Promise<DuckingResult>;
/**
 * Pure builder for the sidechain filter graph. Exposed so tests can verify
 * the chain without spawning ffmpeg.
 */
export declare function buildDuckingFilter(opts?: DuckingOptions): string;
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