What ISOBMFF Specifications Does libavif Support?

This article provides a direct overview of the ISO Base Media File Format (ISOBMFF) specifications that the libavif library adheres to. It covers the core standards, including ISO/IEC 14496-12 and ISO/IEC 23008-12, that define how libavif parses and writes AV1 Image File Format (AVIF) container data.

The Core ISOBMFF Standard: ISO/IEC 14496-12

The libavif library is designed to fully adhere to the ISO/IEC 14496-12 specification, which defines the ISO Base Media File Format (ISOBMFF). Specifically, libavif complies with the structural requirements established in ISO/IEC 14496-12:2015 (5th Edition) and its subsequent revisions, such as the 6th Edition (2020) and 7th Edition (2022).

Because AVIF files are a specialized subset of ISOBMFF, libavif reads and writes the standard box structures defined in this specification, including: * ftyp (File Type Box) * meta (Metadata Box) * iloc (Item Location Box) * iinf (Item Information Box) * iprp (Item Properties Box)

The HEIF Structural Standard: ISO/IEC 23008-12

To support image-specific containers, libavif adheres to ISO/IEC 23008-12 (Information technology — High efficiency coding and media delivery in heterogeneous environments — Part 12: Image File Format). This specification, commonly known as HEIF (High Efficiency Image File Format), is derived directly from the ISOBMFF standard.

Libavif uses the structural rules of ISO/IEC 23008-12 to handle: * Single image items and image collections. * Derived images (such as grids and overlays). * Auxiliary images (such as alpha channels and depth maps). * Associated metadata (Exif and XMP payloads).

The AVIF Specification Integration

While libavif strictly follows the container layout of ISO/IEC 14496-12 and ISO/IEC 23008-12, it binds these formats to the AOM AV1 Image File Format (AVIF) Specification. This specification defines how AV1 compressed video bitstreams are encapsulated as image items within the ISOBMFF structure, ensuring seamless compatibility across modern web browsers and operating systems.