Adobe After Effects CS4 - Manual (Page 237)

231 USING AFTER EFFECTS CS4
Animation and keyframes
Last updated 12/21/2009
More Help topics
“ Expression basics ” on page 646
“ Work area ” on page 201
Online resources for converting audio to keyframes and using the results
Aharon Rabinowitz provides a video tutorial on the Creative COW website that shows how to link the audio amplitude
keyframes to other properties—in this case the properties of the Wave Warp effect, to synchronize animation with
sound.
John Dickinson provides a video tutorial on his Motionworks website that shows how to use the Convert Audio To
Keyframes keyframe assistant to animate the opacity of a layer and one of the properties of the Grid effect to the beat
of the music in a soundtrack.
Satya Meka provides a tutorial and animation preset on his website with which you can generate animations based on
separate audio frequency ranges.
Nathan Gambles provides an expression on the Video Copilot website that ducks (reduces the volume of) audio on one
layer when the volume of audio on another layer increases. This technique is useful, for example, for automatically
decreasing the volume of a soundtrack when dialog occurs. This expression for the Stereo Mixer effect depends on the
Convert Audio To Keyframes keyframe assistant having been applied to the other audio layer.
Keyframe interpolation
About spatial and temporal keyframe interpolation
Interpolation is the process of filling in the unknown data between two known values. You set keyframes to specify a
property’s values at certain key times. After Effects interpolates values for the property for all times between keyframes.
Because interpolation generates the property values between keyframes, interpolation is sometimes called tweening.
Interpolation between keyframes can be used to animate movement, effects, audio levels, image adjustments,
transparency, color changes, and many other visual and audio elements.
After you create keyframes and motion paths to change values over time, you may want to make more precise
adjustments to the way that change occurs. After Effects provides several interpolation methods that affect how the in-
between values are calculated.
Temporal interpolation is the interpolation of values in time; spatial interpolation is the interpolation of values in space.
Some properties—such as Opacity—have only a temporal component. Other properties—such as Position—also have
spatial components.
More Help topics
“ Controlling speed between keyframes ” on page 237
“ The Graph Editor ” on page 211
“ Keyframe interpolation methods ” on page 233
“ Keyframes and the Graph Editor (keyboard shortcuts) ” on page 751
“ Showing properties and groups in the Timeline panel (keyboard shortcuts) ” on page 748