MIAF Profiles for Baseline AVIF Implementations

The AV1 Image File Format (AVIF) is structurally based on the Multi-Image Application Format (MIAF, ISO/IEC 23000-22), which specifies constrained container structures using the ISO Base Media File Format (ISOBMFF). This article explains how baseline AVIF implementations rely directly on MIAF profiles, detailing the required structural brands, video coding constraints, and technical compliance boundaries necessary for standard-compliant AVIF decoders and encoders.

The MIAF Foundation in AVIF

MIAF defines a set of constraints to simplify format handling, reduce decoder complexity, and ensure broad interoperability across multimedia platforms. Rather than creating a container structure from scratch, the Alliance for Open Media (AOMedia) defined AVIF as an explicit application profile of MIAF.

Because of this architectural dependency, every baseline AVIF implementation must directly comply with the core MIAF constraints, while incorporating AV1-specific decoding profiles.

The Baseline MIAF Profile Requirements

In baseline AVIF implementations, MIAF profiles apply through a combination of container-level brands and AV1 video profile limitations:

• The MIAF Brand (miaf): Baseline AVIF files are required to claim compatibility with the general MIAF specification. A fully compliant baseline AVIF file includes the miaf brand in the compatible brands list (ftyp box), alongside the structural mif1 (ISO Multi-Image Format) brand and the AV1-specific avif brand.
• Structural Framing Profile: Baseline AVIF restricts image structure according to MIAF rules. It mandates that images must be represented as either a single primary item or as a collection of grid items. MIAF limits complex presentation scenarios to ensure baseline decoders can reconstruct the image without supporting extensive, dynamic composition graphs.
• Auxiliary Image Profiles (Alpha Channels): MIAF defines how auxiliary images—such as transparency/alpha channels and depth maps—are linked to primary items. Baseline AVIF requires that an auxiliary alpha channel item must share the same pixel aspect ratio and coordinate dimensions as the primary image, adhering directly to MIAF's auxiliary image rules.

Interaction with the AVIF Baseline Profile

AVIF establishes two main profiles: the Baseline Profile and the Advanced Profile. The Baseline Profile maps directly to MIAF requirements under the following parameters:

1. Codec Profile: It mandates the use of the AV1 Main Profile.
2. Bit Depth and Chroma Subsampling: Conformance requires 8-bit or 10-bit pixel depth. Chroma subsampling is limited to 4:2:0 or 4:0:0 (monochrome), keeping baseline decoders simple and uniform with MIAF's primary target profiles.
3. Level Limit: The baseline implementation caps single coded frames at Level 5.1, ensuring maximum image resolutions do not exceed practical decoding thresholds on consumer hardware.

Practical Decoding Implications

For an AVIF implementation to be considered baseline-compliant, the decoder must possess a MIAF-compliant parsing engine capable of handling standard ISOBMFF metadata, image grid configurations, and auxiliary image associations. By relying on the core MIAF profile, baseline AVIF ensures that implementers only need to support a standardized subset of ISOBMFF features alongside an AV1 Main Profile hardware or software decoder.