[AV1] defines the syntax and semantics of an AV1 bitstream. The AV1 Image File Format defined in this document supports the storage of a subset of the syntax and semantics of an AV1 bitstream. Specifically, only bitstreams with the
still_picture flag set to 1 are supported. For some other configurations of AV1 bitstreams, the [AV1-ISOBMFF] specification SHOULD be used.
Is the restriction to have still_picture = 1 necessary?
AV1 Image File Format supports High Dynamic Range (HDR) and Wide Color Gamut (WCG) images as well as Standard Dynamic Range (SDR). It supports monochrome images as well as multi-channel images with all the bit depths and color spaces specified in [AV1].
An AVIF file is designed to be a conformant [HEIF] file for both image items and image sequences. Specifically, this specification follows the recommendations given in "Annex I: Guidelines On Defining New Image Formats and Brands" of [HEIF].
This specification reuses syntax and semantics used in [AV1-ISOBMFF].
The MIAF AV1 profile defined in this specification follows the convention of the [MIAF] specification.
Should this specification also define a structural brand stricter than miaf to profile out some features?
2. Image Items and properties
2.1. AV1 Image Item
When an item is of type av01, it is called an AV1 Image Item, and SHALL obey the following constraints:
- The item data SHALL be the content of a single valid AV1 Sync Sample as defined in [AV1-ISOBMFF] with the additional constraints that there SHALL be only one Sequence Header OBU and it SHALL have its
still_pictureflag set to 1 and SHOULD have its
reduced_still_picture_headerflag set to 1.
- The item SHALL be associated with an AV1 Item Configuration Property.
2.2. Image Item Properties
2.2.1. AV1 Item Configuration Property
Box Type: av1C Property type: Descriptive item property Container: ItemPropertyContainerBox Mandatory (per item): Yes, for an image item of type 'av01' Quantity: One for an image item of type 'av01'
The syntax and semantics of the AV1 Item Configuration Property are identical to those of the AV1CodecConfigurationBox defined in [AV1-ISOBMFF], with the following constraints:
- Sequence Header OBUs SHOULD not be present in the AV1 Item Configuration Property.
- The values of the fields in the AV1CodecConfigurationBox SHALL match those of the Sequence Header OBU in the item data and in the AV1CodecConfigurationBox, if any.
- Metadata OBUs, if present, SHALL match the values given in other item properties, such as the PixelInformationProperty or ColourInformationBox.
2.2.2. Other Item Properties
In addition to the Image Properties defined in [HEIF], such as colr, pixi or pasp, AV1 image items MAY also be associated with clli and mdcv introduced in [MIAF].
In general, it is recommended to use properties instead of Metadata OBUs in the AV1 Item Configuration Property.
3. Image Sequences
An AV1 Image Sequence is defined as a set of AV1 Temporal Units stored in an AV1 track as defined in [AV1-ISOBMFF] with the following constraints:
- The Sequence Header OBUs SHALL have their
still_pictureflag set to 1 and SHOULD have their
reduced_still_picture_headerflags set to 1.
- The track handlers
pictMAY be used.
4. Alpha Image Items and Sequences
An AV1 Alpha Image Item (respectively an AV1 Alpha Image Sequence) is an AV1 Image Item (respectively AV1 Image Sequence) with the following additional constraints:
In [ISOBMFF] or [HEIF] files, if an AV1 Alpha Image Item (respectively. an AV1 Alpha Image Sequence) is used, the
aux_type field of the
AuxiliaryTypeInfoBox) SHALL be set to
urn:mpeg:mpegB:cicp:systems:auxiliary:alpha, as defined in [MIAF].
5. MIAF AV1 Baseline Profile
This section defines the MIAF AV1 Baseline profile of [HEIF], specifically for [AV1] bitstreams, based on the constraints specified in [MIAF] and identified by the brand MiA1.
If the brand
MiA1 is in the list of compatible_brands of a TrackTypeBox or FileTypeBox, the following constraints SHALL be respected:
The following "shared constraints" of [MIAF] apply: self-containment, single-layer, grid-limit, single-track, and matched-duration.
For AV1 images stored as items or in pict tracks, the profile SHALL be the Main Profile and the level SHALL be 6.0 level at Main tier or lower.
For AV1 images stored in video tracks, the profile level SHALL be Main Profile and the level SHALL be 5.1 level at Main tier or lower.