# Metadata datatype definition atom ('dtyp') An atom you use to specify the data type of the metadata key atom’s value. ## Overview A metadata datatype definition atom can be used to specify the data type of the metadata key atom’s value. The type of the metadata datatype definition atom is `‘dtyp’`. The layout of a metadata datatype definition atom is as follows: |Data field |Bytes | |-----------------------------------------------------------------------------------------------------------------|--------| |``doc://com.apple.qtff/documentation/quicktime-file-format/Metadata_datatype_definition_atom/Size`` |4 | |``doc://com.apple.qtff/documentation/quicktime-file-format/Metadata_datatype_definition_atom/Type`` = `'dtyp'` |4 | |``doc://com.apple.qtff/documentation/quicktime-file-format/Metadata_datatype_definition_atom/Datatype_namespace``|4 | |``doc://com.apple.qtff/documentation/quicktime-file-format/Metadata_datatype_definition_atom/Datatype_array`` |variable| The combination of `datatype namespace` and `datatype array` indicate the data type (or structure) of a metadata item value. The `datatype namespace` type indicates the interpretation of the `datatype array` value. This specification defines two `datatype namespace` types: - If `datatype namespace` is `0`, `datatype array` contains a big-endian 32-bit unsigned integer corresponding to a well-known type specified in [Well-known types](/documentation/QuickTime-File-Format/Well-known_types). For example, a well-known type of `1` indicates UTF-8 text and `23` indicates a big-endian 32-bit floating-point number. - If `datatype namespace` is `1`, `datatype array` contains a reverse-address style UTF-8 string indicating an extended data type. This data type namespace type can be used if the data type does not have a corresponding well-known data type. `Datatype array` consists of the bytes of a case-sensitive UTF-8 string without a null (`‘\0’`) terminator. For example, a hypothetical `datatype array` “com.company.my-custom-datatype” could register a custom data type belonging to the owner of the DNS registration “mycompany.com”. A `datatype namespace` other than `0` or `1` may occur in a timed metadata track, perhaps written according to a later version of this specification. Metadata item values with unrecognized data types should be ignored. Even so, some processing is still possible on the metadata item with unrecognized data type, such as copying it between tracks. > Note: New datatype namespaces must be registered with Apple. > Note: Many uses for proprietary or custom metadata data types can be satisfied by using the extended data type namespace type code `1`. This allows the new data type to be specified without registration. The reason to add a custom `datatype namespace` type is to allow an existing numbering or naming scheme from a foreign metadata standard to be used with metadata items. ## Topics ### Data fields [`Size`](/documentation/quicktime-file-format/Metadata_datatype_definition_atom/Size) A 32-bit unsigned integer that indicates the size in bytes of the atom structure. [`Type`](/documentation/quicktime-file-format/Metadata_datatype_definition_atom/Type) A 32-bit unsigned integer value. [`Datatype namespace`](/documentation/quicktime-file-format/Metadata_datatype_definition_atom/Datatype_namespace) A 32-bit identifier describing how to interpret the data type for the value. [`Datatype array`](/documentation/quicktime-file-format/Metadata_datatype_definition_atom/Datatype_array) An array of unsigned 8-bit bytes holding the data type designation for values in timed metadata media samples having this key. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)