import { CacheStrategy } from '../types';
/**
 * In-memory cache implementation using a `Map`.
 *
 * Entries are automatically cleaned up when accessed after expiration.
 *
 * @example
 * ```typescript
 * import { fetchTranscript, InMemoryCache } from 'youtube-transcript-plus';
 * const transcript = await fetchTranscript('dQw4w9WgXcQ', {
 *   cache: new InMemoryCache(1800000), // 30 minutes TTL
 * });
 * ```
 */
export declare class InMemoryCache implements CacheStrategy {
    private cache;
    private defaultTTL;
    /** @param defaultTTL - Default time-to-live in milliseconds. Defaults to 1 hour. */
    constructor(defaultTTL?: number);
    get(key: string): Promise<string | null>;
    set(key: string, value: string, ttl?: number): Promise<void>;
}