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  "title" : "Metadata key declaration atom ('keyd')"
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# Metadata key declaration atom ('keyd')

An atom that holds the key namespace and key value of that namespace for the given values.

## Overview

The metadata key declaration atom holds the key namespace and key value of that namespace for the given values. The type of the metadata key declaration atom is `‘keyd’`.

The layout of a metadata key declaration atom is as follows:

|Data field                                                                                                |Bytes   |
|----------------------------------------------------------------------------------------------------------|--------|
|``doc://com.apple.qtff/documentation/quicktime-file-format/Metadata_key_declaration_atom/Size``           |4       |
|``doc://com.apple.qtff/documentation/quicktime-file-format/Metadata_key_declaration_atom/Type`` = `'keyd'`|4       |
|``doc://com.apple.qtff/documentation/quicktime-file-format/Metadata_key_declaration_atom/Key_namespace``  |4       |
|``doc://com.apple.qtff/documentation/quicktime-file-format/Metadata_key_declaration_atom/Key_value_array``|variable|

## Topics

### Data fields

[`Size`](/documentation/quicktime-file-format/Metadata_key_declaration_atom/Size)

A 32-bit unsigned integer that indicates the size in bytes of the atom structure.

[`Type`](/documentation/quicktime-file-format/Metadata_key_declaration_atom/Type)

A 32-bit unsigned integer value.

[`Key_namespace`](/documentation/quicktime-file-format/Metadata_key_declaration_atom/Key_namespace)

A 32-bit identifier describing the domain and the structure of the key value.

[`Key_value array`](/documentation/quicktime-file-format/Metadata_key_declaration_atom/Key_value_array)

An array of unsigned 8-bit bytes holding the key’s value.


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