An AVMetadataItem object represents an item of metadata associated with an audiovisual asset or with one of its tracks. To create metadata items for your own assets, you use the mutable subclass, AVMutableMetadataItem.
From the iOS Developer Library:
An AVMetadataItem object represents an item of metadata associated with an audiovisual asset or with one of its tracks. To create metadata items for your own assets, you use the mutable subclass, AVMutableMetadataItem.
Metadata items have keys that accord with the specification of the container format from which they’re drawn. Full details of the metadata formats, metadata keys, and metadata key spaces supported by AV Foundation are available among the defines in AVMetadataFormat.h.
You can load values of a metadata item “lazily” using the methods from the AVAsynchronousKeyValueLoading protocol (see “Asynchronous Loading”). The AVAsset class and other classes in turn provide their metadata lazily so that you can obtain objects from those arrays without incurring overhead for items you don’t ultimately inspect.
You can filter arrays of metadata items using the methods of this class. For example, you can filter by key and key space, by locale, and by preferred language.
