Methods, data processing systems and machine readable non-transitory storage media are described that can provide, in one embodiment, a non-time based description of types of metadata in a time based metadata track that can be associated with, in time, a time based media track. The description can include a set of keys, or other identifiers, that specify the types of metadata in the metadata track, and the description can also include values describing the structure of each key and values describing how to interpret each key.