/** Concatenate audio files using ffmpeg's concat demuxer. */
export declare function concatAudio(files: string[], output: string): Promise<void>;
/** Generate a silence MP3 of the given duration in seconds. */
export declare function generateSilence(duration: number, output: string): Promise<void>;
/** Extract an audio segment from a file by start/end times (seconds). */
export declare function extractAudioSegment({ endTime, input, output, startTime, }: {
    input: string;
    startTime: number;
    endTime: number;
    output: string;
}): Promise<void>;
/** Extract the audio track from a video file and re-encode to MP3. */
export declare function extractVideoAudio(input: string, output: string): Promise<void>;
/**
 * Normalize audio to EBU R128 standard using ffmpeg-normalize. Returns the path
 * to the normalized file. Skips if already exists.
 */
export declare function normalizeAudio(input: string): Promise<string>;
/**
 * Source-of-truth for our standard H.264 / AAC video encode profile. Use these
 * named values when calling APIs that take typed options (e.g. Remotion's
 * `renderMedia`, which surfaces some flags as `codec` / `x264Preset` / `crf` /
 * `pixelFormat` / `audioCodec` / `audioBitrate`). For direct ffmpeg shell-out,
 * use the pre-flattened arg arrays below.
 *
 * The settings are tuned for concat-safe output:
 *
 * - `gop` of 30 puts a keyframe every 1s at 30fps, required for seekability and
 *   `-c:v copy` concat
 * - `bFrames: 0` prevents non-monotonic DTS at concat seams
 * - `videoTrackTimescale` of 90000 matches Remotion's default timebase
 */
export declare const VIDEO_ENCODE_SETTINGS: {
    readonly videoCodec: "libx264";
    /**
     * Value for Remotion's `codec` option (which uses short names, not ffmpeg
     * codec ids).
     */
    readonly remotionCodec: "h264";
    readonly crf: 23;
    readonly x264Preset: "medium";
    readonly gop: 30;
    readonly bFrames: 0;
    readonly pixelFormat: "yuv420p";
    readonly videoTrackTimescale: 90000;
    readonly audioCodec: "aac";
    readonly audioSampleRate: 48000;
    readonly audioBitrate: "128k";
};
/**
 * Ffmpeg args for H.264 video encoding (concat-safe). Includes `-movflags
 * +faststart` so the muxed MP4 supports progressive HTTP playback.
 */
export declare const VIDEO_ENCODE_ARGS: string[];
/** Standard AAC audio encode args to pair with {@link VIDEO_ENCODE_ARGS}. */
export declare const VIDEO_AUDIO_ENCODE_ARGS: string[];
/**
 * Args for use inside Remotion's `ffmpegOverride` — just the flags that
 * `renderMedia`'s typed options don't surface natively. Currently only `-bf 0`
 * (no B-frames), which prevents non-monotonic DTS at concat seams between
 * Remotion-rendered clips and the B-frame-free training videos compressed by
 * {@link compressVideo}. Pair with the typed options fed from
 * {@link VIDEO_ENCODE_SETTINGS} for a render that matches our standard profile.
 *
 * Example:
 *
 *     renderMedia({
 *       codec: VIDEO_ENCODE_SETTINGS.remotionCodec,
 *       x264Preset: VIDEO_ENCODE_SETTINGS.x264Preset,
 *       crf: VIDEO_ENCODE_SETTINGS.crf,
 *       pixelFormat: VIDEO_ENCODE_SETTINGS.pixelFormat,
 *       audioCodec: VIDEO_ENCODE_SETTINGS.audioCodec,
 *       audioBitrate: VIDEO_ENCODE_SETTINGS.audioBitrate,
 *       ffmpegOverride: ({ args }) => {
 *         const out = args[args.length - 1]
 *         const yflag = args[args.length - 2]
 *         return [...args.slice(0, -2), ...VIDEO_REMOTION_OVERRIDE_ARGS,
 *         yflag, out]
 *       },
 *       ...
 *     })
 */
export declare const VIDEO_REMOTION_OVERRIDE_ARGS: string[];
/**
 * Compress a video using the standard H.264 settings. If `audio` is provided,
 * its track replaces the source video's audio.
 */
export declare function compressVideo({ input, output, audio, }: {
    input: string;
    output: string;
    audio?: string;
}): Promise<void>;
/**
 * Mix narration audio with background music at a fixed volume ratio. Music is
 * trimmed to the shorter of the two inputs; if `targetDuration` is provided,
 * the output is padded with silence to match exactly.
 */
export declare function mixAudioWithMusic({ music, narration, output, targetDuration, }: {
    narration: string;
    music: string;
    output: string;
    targetDuration: number;
}): Promise<void>;
/** Get the duration of an audio file in seconds using ffprobe. */
export declare function getDurationFromFile(file: string): Promise<number>;