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

Some Useful Examples and ScenariosCreating an Effect DescriptionFigure 6-5 (page 340) shows the set of atoms that must be added to the entry description.Figure 6-5An example effect description for the Push effectRequired atomsByteUse the effect component withthe name 'push'.kParameterWhatName'push'1The first source is 'srcA'which is the name of a sourcedefined in the input map.kEffectSourceName'srcA'1The second source is 'srcB'from the input map.kEffectSourceName'srcB'2The percentage value, whichis tweened for 25% to 75%.Parameter atoms'pcnt''srcB'kTweenTypekParamTypeDataFixed11kTweenData0.250.751The direction from which thesecond source pushes thefirst. The value 2 indicatesit pushes in from below.'from'21An important property of effect parameters is that most can be tweened (and some must be tweened). Tweeningis QuickTime’s general purpose interpolation mechanism (see “Tween Media” (page 235) for more information).For many parameters, it is desirable to allow the value of the parameter to change as the effect executes. Inthe example shown in Figure 6-5 (page 340), the 'pcnt' parameter must be a tween. This parameter controlswhich frame of the effect is rendered at any given time, so it must change for the effect to progress. The 'from'parameter is not a tween in the example above, but it could be if we wanted the direction of the push tochange during the course of the effect.Creating an Input MapThe input map is another QT atom container that you attach to the effects track. It describes the sources usedin the effect and gives a name to each source. This name is used to refer to the source in the effects description.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.340