# Timed metadata sample description An atom that defines how to interpret timed metadata media samples. ## Overview The timed metadata sample description contains information that defines how to interpret timed metadata media samples. This sample description is based on the standard sample description header, as described in [`Sample description atom`](/documentation/quicktime-file-format/Sample_description_atom). The metadata sample description is a derived sample description format which describes metadata values represented in atoms. It may also include other atoms not holding metadata values. Zero, one, or more values may be carried in a metadata sample description for a particular time. The data format field contains the format of the timed metadata media, which is set to `'mebx'`. > Note: Other forms of timed metadata media are not described here. They would be indicated by an alternative type code in the place of `‘mebx’`. The metadata sample description must contain a metadata key table atom and optionally contains a bit rate atom following the standard sample description atom header, defined below. Other atoms may be introduced in the future. - Metadata key table: An atom containing a table of keys and mappings to payload data in the corresponding timed metadata media samples. - Bit rate atom: An optional atom that contains data that signals the bit rate of a media stream. ## Topics ### Describing timed metadata [`Metadata key table atom ('keys')`](/documentation/quicktime-file-format/Metadata_key_table_atom) An atom that contains a table of keys and mappings to payload data in the corresponding timed metadata media samples. [`Bit rate atom ('btrt')`](/documentation/quicktime-file-format/Bit_rate_atom) An atom that signals the bit rate information of a stream. [`Metadata key atom`](/documentation/quicktime-file-format/Metadata_key_atom) An atom that contains a key that corresponds to the timed metadata track containing it. [`Metadata key declaration atom ('keyd')`](/documentation/quicktime-file-format/Metadata_key_declaration_atom) An atom that holds the key namespace and key value of that namespace for the given values. [`Metadata datatype definition atom ('dtyp')`](/documentation/quicktime-file-format/Metadata_datatype_definition_atom) An atom you use to specify the data type of the metadata key atom’s value. [`Metadata locale atom ('loca')`](/documentation/quicktime-file-format/Metadata_locale_atom) An atom that tags a metadata value with a locale. --- 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)