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

Media Data Atom TypesSprite Track Media FormatImportant Some sprite track property atoms were added in QuickTime 4. In particular, you must set thekSpriteTrackPropertyHasActions track property in order for your sprite actions to be executed.Sprite Track Property AtomsThe following constants represent atom types for sprite track properties. These atoms are applied to the wholetrack, not just to a single sample.Constant DescriptionskSpriteTrackPropertyHasActionsYou must add an atom of this type with its leaf data set to true if you want the movie controller toexecute the actions in your sprite track’s media. The atom’s leaf data is of type Boolean. The defaultvalue is false, so it is very important to add an atom of this type if you want interactivity to take place.kSpriteTrackPropertyQTIdleEventsFrequencyYou must add an atom of this type if you want the sprites in your sprite track to receive kQTEventIdleQuickTime events. The atom’s leaf data is of type UInt32. The value is the minimum number of ticksthat must pass before the next QTIdle event is sent. Each tick is 1/60th of one second. To specify “Idleas fast as possible,” set the value to 0. The default value is kNoQTIdleEvents, which means don’t sendany idle events.It is possible that for small idle event frequencies, the movie will not be able to keep up, in which caseidle events will be sent as fast as possible.Since sending idle events takes up some time, it is best to specify the largest frequency that producesthe results that you desire, or kNoQTIdleEvents if you do not need them.kSpriteTrackPropertyVisibleYou can cause the entire sprite track to be invisible by setting the value of this Boolean property tofalse. This is useful for using a sprite track as a hidden button track—for example, placing an invisiblesprite track over a video track would allow the characters in the video to be clickable. The default valueis visible (true).kSpriteTrackPropertyScaleSpritesToScaleWorldYou can cause each sprite to be rescaled when the sprite track is resized by setting the value of thisBoolean property to true. Setting this property can improve the drawing performance and quality ofa scaled sprite track. This is particularly useful for sprite images compressed with codecs that areresolution-independent, such as the Curve codec. The default value for this property is false.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.214