Macromedia flex 2 Manual

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About tween effects
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You can now pass the URL of an MP3 to the effect, as the following example shows:
<?xml version="1.0"?>
<!-- effects/MainSoundEffectParam.mxml -->
<mx:Application xmlns:mx="http://www.adobe.com/2006/mxml" 
    xmlns:MyComps="myEffects.*"> 
    <MyComps:MySoundParam id="mySoundEffect" 
        soundMP3="http://localhost:8100/flex/assets/sample.mp3"/>
    <!-- Use the SoundEffect effect with a mouseOver trigger. -->
    <mx:Label text="play MP3" rollOverEffect="mySoundEffect"/>
    
</mx:Application>
About tween effects 
Most Flex effects are implemented by using the tweening mechanism, where a tween defines a 
transition performed on a target object over a period of time. That transition could be a 
change in size, such as the 
Zoom
 or 
Resize
 effects perform; a change in visibility, as the Fade 
or Dissolve effects perform; or other types of transition. 
You use the following classes to implement a tween effect: 
mx.effects.Tween
A class used to implement tween effects. A Tween object accepts a start 
value, an end value, and an optional easing function. When you define tween effect classes, 
you create an instance of the Tween class in your override of the 
Effect.play()
 method. 
The Tween object invokes the 
mx.effects.TweenEffect.onTweenUpdate()
 callback 
method on a regular interval, passing the callback method an interpolated value between the 
start and end values. Typically, the callback method updates some property of the target 
component, causing that component’s property to animate over time. For example, the Move 
effect modifies the 
x
 and 
y
 properties of the target component for the duration of the effect to 
show an animated movement.
When the effect ends, the Tween object invokes the 
mx.effects.TweenEffect.onTweenEnd()
 callback method. This method performs any final 
processing before the effect terminates. You must call 
super.onTweenEnd()
 from your 
override.
mx.effects.TweenEffect
The base factory class for all tween effects. This class encapsulates 
methods and properties that are common among all Tween-based effects. 
mx.effects.effectClasses.TweenEffectInstance
The instance class for all tween effects.