Items

The ISO base media file format (ISO/IEC 14496-12) defines an item model within the MetaBox for storing non-timed data such as images, metadata documents, and derived content. Each item is described by an ItemInfoEntry that declares its item_type — a four-character code identifying the format of the item's data.

Items can be associated with properties and linked to other items through typed references, enabling complex relationships such as thumbnails, auxiliary images, and derived image constructions.

Item types

The item_type in the ItemInfoEntry identifies the coding format or role of an item. For example, an HEVC coded image uses item type hvc1, while Exif metadata uses Exif.

Item properties

Item properties are small data records stored in the ItemPropertyContainerBox ('ipco') and associated with items via the ItemPropertyAssociation ('ipma'). Each property is identified by its box type and provides descriptive or transformative metadata for the associated item (e.g., image dimensions, rotation, colour information).

Item references

Item references in the ItemReferenceBox ('iref') define typed links between items. Each reference type is a four-character code indicating the relationship (e.g., thmb for thumbnail, dimg for derived image source, auxl for auxiliary image).