Quicktime File Format (2012-08-14).pdf

MetadataExtensibilityTypeA 32-bit unsigned integer value set to 'mdhr'VersionOne byte that is set to 0.FlagsThree bytes that are set to 0.nextItemIDA 32-bit unsigned integer indicating the value to use for the item ID of the next item created or assignedan item ID. If the value is all ones, it indicates that future additions will require a search for an unuseditem ID.Note If the last metadata item with an item information atom is removed and value of nextItemIDis 0xFFFFFFFF, an implementation may reset the metadata header atom’s nextItemID value to 0 sothat new assignments are again efficient (that is, they do not require a search for unused identifiers).ExtensibilityIn order to allow metadata to be rewritten easily and without the need to rewrite the entire QuickTime moviefile, free space atoms may occur anywhere in the definition of the metadata atom between the positions ofother atoms contained by the metadata atom. Free space atoms may not be inserted between items in themetadata item list atom or within atoms in the metadata item list atom. This restriction on free space atomdefinition avoids the risk of confusing a free space atom with a meaning of a ‘free’ identifier or a value atomof type ‘free’ defined in the context of the metadata atom structure.Similarly, UUID atoms for specific extensions may be placed in any position where a succession of atoms ispermitted. Note that UUID atoms should not be created for atoms already defined using four-character codes.Unrecognized atoms (that is, those atoms whose types not defined in the context of the metadata atomstructure and are contained within the metadata item list atom) are ignored.Localization List SetsWhen metadata items have individual values associated with more than one country or more than one language,a country list atom and/or language list atom are required. Alternatively, if all values are associated with zeroor one country, no country list atom is required, and if all values are associated with zero or one language, nolanguage list atom is required.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.132