export declare class FileEncoder {
    /** "data:image/png;base64,iVBOR..." → "iVBOR..." */
    static stripDataUrlPrefix(base64: string): string;
    /** Estimate decoded size from base64 string length */
    static getDecodedSizeBytes(base64: string): number;
    static validateFileSize(base64: string, maxSizeMB: number): boolean;
    /** Detect MIME from data URL prefix or magic bytes */
    static detectMimeType(base64: string): string;
    static toBuffer(base64: string): Buffer;
}