/**
 * Wrap AV1 still pictures in an AVIF/HEIF container.
 *
 * With `alphaData`, the file holds two `av01` items: the colour image (item 1,
 * primary) and its alpha (item 2), which an `auxl` reference ties to item 1
 * and an `auxC` property marks as alpha. Without it, a single item as before.
 */
export declare function writeAvif(av1Data: Uint8Array, width: number, height: number, alphaData?: Uint8Array): Uint8Array;
/**
 * The URN an auxiliary image carries to say "I am this image's alpha"
 * (ISO/IEC 23008-12 / MIAF). Every AVIF decoder keys transparency off it.
 */
export declare const ALPHA_URN: 'urn:mpeg:mpegB:cicp:systems:auxiliary:alpha';