/**
 * Narration (TTS) generation.
 *
 * `generateNarration` synthesizes a single narration clip for a project from a
 * text script via a TTS backend (from the audio-platform registry), writes the
 * audio to `projects/<slug>/artifacts/audio/narration.wav`, and persists a
 * `narration.json` artifact describing it. When a `videoDurationMs` is supplied,
 * the artifact also embeds a pure `planNarrationFit()` plan (atempo / loop-video
 * timing) so a downstream assemble step can fit the narration to the video bed.
 *
 * Pure-ish: `env` and `fetcher` are threaded through to the backend so tests
 * run fully offline with no real keys or network. Throws `tts_failed` when no
 * requested/available TTS backend can run.
 */
import type { NarrationFitPlan } from './assemble/narration-fit.js';
export declare const NARRATION_SCHEMA_VERSION = 1;
export interface NarrationArtifact {
    schemaVersion: typeof NARRATION_SCHEMA_VERSION;
    projectSlug: string;
    generatedAt: string;
    backendId: string;
    voice?: string;
    text: string;
    /** Project-relative path to the generated narration audio. */
    path: string;
    durationMs: number;
    /**
     * Backends that failed (in order) before `backendId` succeeded, when the
     * automatic fallback chain was used. Omitted when the first backend succeeded
     * or an explicit `--backend` was given (explicit selection never falls back).
     */
    fallbackFrom?: string[];
    /** Present only when a videoDurationMs was supplied. */
    fit?: NarrationFitPlan;
}
export interface GenerateNarrationOptions {
    workspaceRoot: string;
    slug: string;
    text: string;
    voice?: string;
    /** Restrict to this backend id (defaults to the first AVAILABLE backend). */
    backendId?: string;
    /** When given, embed a planNarrationFit() plan in the artifact. */
    videoDurationMs?: number;
    dryRun?: boolean;
    env?: NodeJS.ProcessEnv;
    fetcher?: typeof fetch;
}
export declare function narrationArtifactPathFor(root: string, slug: string): string;
export declare function narrationAudioDirFor(root: string, slug: string): string;
export declare function readNarrationArtifact(root: string, slug: string): Promise<NarrationArtifact | null>;
/**
 * Generate a single narration clip + persist the `narration.json` artifact.
 * Returns the written artifact. Throws `tts_failed` when no requested/available
 * TTS backend can run.
 */
export declare function generateNarration(options: GenerateNarrationOptions): Promise<NarrationArtifact>;
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