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

Profile Atom GuidelinesUniversal Featuresfeature-codeA four-character code either documented here (universal features), or in the specification identified bythe brand. The value of 0 is reserved for an empty slot with no meaningful feature-value.feature-valueEither a value from an enumerated set (for example, 1 or 0 for true or false, or an MPEG-4 profile-levelID) or a value that can compared (for example, bit rate as an integer or dimensions as a 32-bit packedstructure).The profile atom is a full atom, so it has an 8-bit version and 24 bits of flags. For this specification, the versionis 0 and the flags have the value 0. A reader compliant with this specification should treat any profile atomwith a nonzero version value as if it did not exist.Figure F-2 (page 397) shows the layout of a typical feature.Figure F-2Layout of a typical featureBytesReserved = 0x00000000Part ID = ' '(0x20202020)Feature Code = 'avbr'444Value = 0x000000014Universal FeaturesA feature consists of four fields: a reserved field, which is set to zero; a part-ID, which specifies which brandthe feature belongs to; a feature code, which identifies the feature; and a value field, which holds the featurevalue).The part-ID can be either universal or brand-specific. Universal features have a part-ID of four ASCII spaces(0x20202020). Brand-specific features have a part-ID for a particular brand, which is taken from theCompatible_brands field of the file type atom. Brand-specific features of QuickTime files have a part-ID of 'qt'. All features listed in this section are universal features; that is, they can be used in any file that includes aprofile atom.It is permissible to use the feature code of 0x00000000 as a placeholder, paired with a feature value of0x00000000 for one or more features. Readers should simply ignore features having a feature code of zero.No feature will exist to describe the unit of other features, such as bit rate. The device should consider themagnitude and tailor its display appropriately.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.397