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

Media Data Atom TypesSprite Media Atom and Data TypeskSpriteStatusStringsBehaviorAtomTypeSpecifies an ID of a string variable contained in a sprite track to display in the status area of the browser.Note All sprite media—specifically the leaf data in the QT atom containers for sample and sprite track properties—shouldbe written in big-endian format.kSpriteUsesImageIDsAtomTypeThis atom allows a sprite to specify which images it uses—in other words, the subset of images that itsimageIndex property can refer to.You add an atom of type kSpriteUsesImageIDsAtomType as a child of a kSpriteAtomType atom,setting its leaf data to an array of QT atom IDs. This array contains the IDs of the images used, not theindices.Although QuickTime does not currently use this atom internally, tools that edit sprite media can use theinformation provided to optimize certain operations, such as cut, copy, and paste.kSpriteImageRegistrationAtomTypeSprite images have a default registration point of 0, 0. To specify a different point, you add an atom oftype kSpriteImageRegistrationAtomType as a child atom of the kSpriteImageAtomType andset its leaf data to a FixedPoint value with the desired registration point.kSpriteImageGroupIDAtomTypeYou must assign group IDs to sets of equivalent images in your key frame sample. For example, if thesample contains ten images where the first two images are equivalent, and the last eight images areequivalent, then you could assign a group ID of 1000 to the first two images, and a group ID of 1001 tothe last eight images. This divides the images in the sample into two sets. The actual ID does not matter;it just needs to be a unique positive integer.Each image in a sprite media key frame sample is assigned to a group. You add an atom of typekSpriteImageGroupIDAtomType as a child of the kSpriteImageAtomType atom and set its leaf datato a long containing the group ID.Important You must assign group IDs to your sprite sample if you want a sprite to display images withnon-equivalent image descriptions (that is, images with different dimensions).You use the following atom types, which were added to QuickTime 4, to specify that an image is referencedand how to access it.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.218