# Overview of timed metadata Synchronize metadata references to media tracks for particular media time periods with timed metadata. ## Overview A timed metadata track synchronizes metadata references to media tracks for particular media time periods through the track reference, edit, and edit list structures. It is a specialization of the track structure which uses the base media information atom of type `‘minf’`, and a track handler type value set to `‘meta’`. The base media information atom contains the generic media header atom of type `‘gmhd’`. Because a metadata track is neither visual nor aural, the following track properties should have these values: - Track width and track height each set to `0`. - The track volume set to `0`. - The track matrix set to the identity matrix. A QuickTime movie can contain none, one, or several timed metadata tracks. Timed metadata tracks can refer to multiple tracks. Metadata tracks are linked to the tracks they describe using a track-reference of type `‘cdsc’`. The metadata track holds the `‘cdsc’` track reference. If a metadata track describes characteristics of the entire movie, there should be no track reference of type `'cdsc'` between it and another track. These metadata tracks can be considered to hold global metadata for the movie. Using a timed metadata track, any form of descriptive metadata that changes over time can be linked to a range of media times for which it is valid. Examples of timed metadata can include: - Faces detected in the scene - Location-based information (such as GPS) - Camera aperture and other changing camera-related information - Copyright and other information for individual clips edited together - Information such as scene changes and actor names added to the movie in production As with other tracks, each metadata sample is associated with a single timed metadata sample description. This sample description signals information needed to interpret the data in the metadata sample in a way that is analogous to how a video track’s video sample atom indicates that video samples contain H.264 compressed sample data of particular dimensions. Zero, one, or many metadata values can be associated with a range of media time in the track. The accommodation for no metadata values for a time allows runs of time with metadata interspersed with runs of time with no metadata. Because the timed metadata is organized as a track, it is also possible to use track edits to indicate the absence of metadata. For some situations, however, it would be better to include metadata samples that themselves carry no metadata values. --- 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)