/**
 * Configuration options for the audio mixer
 */
export interface AudioMixerConfig {
    /** Gain level for the background music (0.0 to 1.0) */
    musicGain?: number;
    /** Duration of fade transition when changing music (in milliseconds) */
    fadeDuration?: number;
}
/**
 * Represents an active audio mixing session
 */
export interface AudioMixerSession {
    /** The output MediaStream containing mixed audio and optional video */
    outputStream: MediaStream;
    /** Update the background music gain (0.0 to 1.0) */
    setMusicGain: (gain: number) => void;
    /** Change the background music with optional fade transition */
    changeMusic: (musicUrl: string, withFade?: boolean) => Promise<void>;
    /** Stop the background music with optional fade out */
    stopMusic: (withFade?: boolean) => Promise<void>;
    /** Completely cleanup and stop the mixing session */
    cleanup: () => void;
}
/**
 * Create an audio mixing session that combines a MediaStream with background music.
 * The input stream's audio is kept at maximum gain, while the music gain is configurable.
 * Any video tracks from the input stream are preserved in the output.
 *
 * @param inputStream - MediaStream containing at least one audio track (and optionally video)
 * @param musicUrl - Optional URL or path to the MP3 music file. If not provided, the mixer is transparent.
 * @param config - Configuration options (musicGain defaults to 0.5, fadeDuration to 1000ms)
 * @returns AudioMixerSession with the output stream and control methods
 *
 * @example
 * ```typescript
 * // Create a transparent mixer (no music initially)
 * const session = await createAudioMixer(userMediaStream);
 *
 * // Or start with music
 * const session = await createAudioMixer(
 *   userMediaStream,
 *   'background-music.mp3',
 *   { musicGain: 0.3, fadeDuration: 2000 }
 * );
 *
 * // Use the mixed output
 * videoElement.srcObject = session.outputStream;
 *
 * // Start or change music with fade (default)
 * await session.changeMusic('new-song.mp3');
 *
 * // Change music without fade (instant switch)
 * await session.changeMusic('another-song.mp3', false);
 *
 * // Adjust volume
 * session.setMusicGain(0.5);
 *
 * // Stop music with fade (default)
 * await session.stopMusic();
 *
 * // Stop music instantly
 * await session.stopMusic(false);
 *
 * // Cleanup when done
 * session.cleanup();
 * ```
 */
export declare function createAudioMixer(inputStream: MediaStream, musicUrl?: string, config?: AudioMixerConfig): Promise<AudioMixerSession>;
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