The additional attributes supplied by the metadata item.
- iOS 4.0+
- macOS 10.7+
- Mac Catalyst 13.0+
- tvOS 9.0+
- watchOS 6.0+
Extra attributes, when they are present, are specific to metadata container formats and keys in their associated key-spaces. For example, the "attached picture" frame defined by the ID3 tag specification can be represented by an
AVMetadata with keyspace
id3Metadata, a value that carries the image data, and extra attributes that include a description of the picture as carried in the 'APIC' frame of the ID3 tag.