Given a starting value and an ending value, QuickTime is able to figure out, for any moment in the duration of the animation, what the appropriate value between those two values should be. This process is called tweening, and the track that contains the information needed to do the tweening is called a .
QuickTime provides support for either simple linear interpolations of data or more complex tweening operations and operations. For instance, the various types of path tweens allow us to derive values based on the shape of an arbitrary curve defined by a vector path. And the list tween derives values from a list of atoms in an atom container, which can result in a series of discrete steps of non–continuous values. Anyway, QTPlugin currently supports only linear interpolations of numerical or graphical data.
The QTPlugin provides the developers with the Tween Framework to add tween–based animation to their applications. The Tween Framework, which is a set of classes, handles all the tasks necessary to provide tweening by using either or auto–running .
The QTPlgTweenMediaDesc class is part of the Tween Framework and defines the sample description object you have to associate to the tween samples when adding them to a . Also, you obtain instances of this class when inspecting the of an existing tween track.
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The QTPlgTweenMediaDesc class constructors are called when you create a new instance of the class, while the ˜QTPlgTweenMediaDesc class destructor, is called automatically when the class is no more in use. Also, you can invoke the class destructor by setting the instance of the class to nil.
Once a new class instance is returned, it is good practice to check the class property to be sure that the new object can be used. See the validity requirements of the for more details.
The class provides you with the following initializer methods: