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Term: Wrapper

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Term: Wrapper


A term often used by digital content specialists to name a file format that encapsulates its constituent bitstreams and includes metadata that describes the content within. Archetypal examples include WAVE and TIFF. Files that are instances of these wrappers are distinguished in terms of their underlying bitstreams, e.g., WAVE files may contain (a) linear pulse code modulated (LPCM) audio, (b) highly compressed audio as used for digital telephony, or (c) other representations of sound. Meanwhile, the self-describing, content-declaring feature of a wrapper is typified by the familiar TIFF header. Relatively more complex and facile wrappers like QuickTime may contain multiple objects, e.g., one or more video streams and separate audio streams.

Wrappers are often specific to a content category but they may be members of a class defined by a more generic specification. For example, the sound format WAVE is an instance of the Microsoft RIFF class, which also includes the video format AVI.

There are a number of formats that do not represent wrapper archetypes like the ones mentioned above. For example, AAF and MXF are two closely related formats employed in television and motion picture production. Video and motion picture creators often call these formats wrappers but they feature some of the characteristics associated with self-describing bundling formats. The metadata in an AAF or MXF file, for example, may reference video and audio content that exists as a separate entity as well as content that is encapsulated within the file.

See also:
Bundling file format