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

GlossaryAAC Advanced Audio Coding (AAC) is astandardized, lossy compression and encodingscheme for digital audio. AAC generally achievesbetter sound quality than MP3 encoding at similarbit rates.alpha channel The upper bits of a display pixel,which control the blending of video and graphicalimage data for a video digitizer component.alternate group A set of related movie tracks(alternate tracks) that contain the same alternategroup identifier in the track header.alternate track A movie track that containsalternate data for another track. QuickTime choosesone track from an alternate group to be used whenthe movie is played. The choice may be based onsuch considerations as image quality or localization.See also track.API (Application Programming Interface) The setof function calls, data structures, and otherprogramming elements by which a structure of code(such as a system-level toolbox) can be accesses byother code (such as an application program).atom The basic unit of data in a movie resource,sprite, or other QuickTime data structure. There area number of different atom types. There are twovarieties of atoms: QT atoms, which may containother atoms, and classic atoms, which do not containany other atoms. See also movie resource, sprite ,QT atom, and classic atom.atom ID A 32-bit integer that uniquely identifiesan atom among other child atoms of the sameparent atom. The root atom has an atom ID value of0x0001. See also child atom, parent atom , and rootatom.atom type A 32-bit value that uniquely identifiesthe data type of an atom. It is normally an OSType,rendered by four ASCII characters. An atom’s datatype helps determine how the atom’s contents areinterpreted.audio track An alternative name for the sound trackfor a QuickTime file. See sound track.background color The color of the backgroundbehind a sprite or other image.bit depth The number of bits used to encode thecolor of each pixel in a graphics buffer.chapter list A set of named entry points into amovie, presented to the viewer as a text list.child atom A QT atom inside a container atom,which is its parent atom. See also QT atom, containeratom , and parent atom.chunk A collection of sample data in a media.Chunks, which may contain one or more samples,allow optimized data access. Chunks in a media mayhave different sizes, and the samples within a chunkmay have different sizes.atom container A tree-structured hierarchy of QTatoms. See also QT atom.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.436