Property attributes and methods (expression reference)

value
Return type: Number, Array, or String.

Returns the value of a property at the current time.

valueAtTime(t)
Return type: Number or Array.

Argument type: t is a Number.

Returns the value of a property at the specified time, in seconds.

For example, to have a property value for each frame chosen randomly from a set of four values, set your four values as keyframes at 0, 1, 2, and 3 seconds, and then apply the following expression to the property:

  valueAtTime(random(4))
Note: Dan Ebberts provides more examples and techniques for using the valueAtTime and velocityAtTime methods on his MotionScript website.

velocity
Return type: Number or Array.

Returns the temporal velocity value at the current time. For spatial properties, such as Position, it returns the tangent vector value. The result is the same dimension as the property.

velocityAtTime(t)
Return type: Number or Array.

Argument type: t is a Number.

Returns the temporal velocity value at the specified time.

speed
Return type: Number.

Returns a 1D, positive speed value equal to the speed at which the property is changing at the default time. This element can be used only for spatial properties.

speedAtTime(t)
Return type: Number.

Argument type: t is a Number.

Returns the spatial speed value at the specified time.

wiggle(freq, amp, octaves=1, amp_mult=.5, t=time)
Return type: Number or Array.

Argument type: freq, amp, octaves, amp_mult, and t are Numbers.

Randomly shakes (wiggles) the value of the property.

freq value is the frequency in wiggles per second.

amp value is the amplitude in units of the property to which it is applied.

octaves is the number of octaves of noise to add together. This value controls how much detail is in the wiggle. Make this value higher than the default of 1 to include higher frequencies or lower to include amplitude harmonics in the wiggle.

amp_mult is the amount that amp is multiplied by for each octave. This value controls how fast the harmonics drop off. The default is 0.5; make it closer to 1 to have the harmonics added at the same amplitude as the base frequency, or closer to 0 to add in less detail.

t is the base start time. This value defaults to the current time. Use this parameter if you want the output to be a wiggle of the property value sampled at a different time.

Example: position.wiggle(5, 20, 3, .5) produces about 5 wiggles per second with an average size of about 20 pixels. In addition to the main wiggle, two more levels of detailed wiggles occur with a frequency of 10 and 20 wiggles per second, and sizes of 10 and 5 pixels, respectively.

This example, on a two-dimensional property such as Scale, wiggles both dimensions by the same amount:

  v = wiggle(5, 10); 
  [v[0], v[0]]

This example, on a two-dimensional property, wiggles only along the y axis:

  freq = 3; 
  amp = 50; 
  w = wiggle(freq,amp); 
  [value[0],w[1]];

Paul Tuersley provides a script on the AE Enhancers forum that automatically adds wiggle, smooth, and loop expressions to selected properties.

Dan Ebberts provides an example expression and a detailed explanation on his MotionScript website that shows how to use the time parameter of the wiggle method to create a looping animation.

temporalWiggle(freq, amp, octaves=1, amp_mult=.5, t=time)
Return type: Number or Array.

Argument type: freq, amp, octaves, amp_mult, and t are Numbers.

Samples the property at a wiggled time. The freq value is the frequency in wiggles per second, amp is the amplitude in units of the property to which it is applied, octaves is the number of octaves of noise to add together, amp_mult is the amount that amp is multiplied by for each octave, and t is the base start time. For this function to be meaningful, the property it samples must be animated, because the function alters only the time of sampling, not the value. Example: scale.temporalWiggle(5, .2)

smooth(width=.2, samples=5, t=time)
Return type: Number or Array.

Argument type: width, samples, and t are Numbers.

Smooths the property values over time, converting large, brief deviations in the value to smaller, more evenly distributed deviations. This smoothing is accomplished by applying a box filter to the value of the property at the specified time. The width value is the range of time (in seconds) over which the filter is averaged. The samples value is the number of discrete samples evenly spaced over time; use a larger value for greater smoothness (but decreased performance). Generally, you’ll want samples to be an odd number so that the value at the current time is included in the average. Example: position.smooth(.1, 5)

loopIn(type="cycle", numKeyframes=0)
Return type: Number or Array.

Loops a segment of time that is measured from the first keyframe on the layer forward toward the Out point of the layer. The loop plays from the In point of the layer. The numKeyframes value determines what segment is looped: The segment looped is the portion of the layer from the first keyframe to the numKeyframes+1 keyframe. For example, loopIn("cycle", 3) loops the segment bounded by the first and fourth keyframes. The default value of 0 means that all keyframes will loop.

You can use keyframe-looping methods to repeat a series of keyframes. You can use these methods on most properties. Exceptions include properties that can’t be expressed by simple numeric values in the Timeline panel, such as the Source Text property, path shape properties, and the Histogram property for the Levels effect. Keyframes or duration values that are too large are clipped to the maximum allowable value. Values that are too small result in a constant loop.

loop type

result

cycle

(default) Repeats the specified segment.

pingpong

Repeats the specified segment, alternating between forward and backward.

offset

Repeats the specified segment, but offsets each cycle by the difference in the value of the property at the start and end of the segment, multiplied by the number of times the segment has looped.

continue

Does not repeat the specified segment, but continues to animate a property based on the velocity at the first or last keyframe. For example, if the last keyframe of a Scale property of a layer is 100%, the layer continues to scale from 100% to the Out point, instead of looping directly back to the Out point. This type does not accept a keyframes or duration argument.

Todd Kopriva provides an example project on his blog that demonstrates the use of the loopIn and loopOut methods, and all of the loop types.

Paul Tuersley provides a script on the AE Enhancers forum that automatically adds wiggle, smooth, and loop expressions to selected properties.

loopOut(type="cycle", numKeyframes=0)
Return type: Number or Array.

Loops a segment of time that is measured from the last keyframe on the layer back toward the In point of the layer. The loop plays until the Out point of the layer. The segment to loop is determined by the specified number of keyframes. The numKeyframes value sets the number of keyframe segments to loop; the specified range is measured backward from the last keyframe. For example, loopOut("cycle", 1) loops the segment bounded by the last keyframe and second-to-last keyframe. The default value of 0 means that all keyframes will loop. See the entry for loopIn for more information.

David Van Brink provides an instructional article and sample project on his omino pixel blog that show how to use the Echo effect, the Particle Playground effect, and the loopOut method to animate a swarm of stylized swimming bacteria.

loopInDuration(type="cycle", duration=0)
Return type: Number or Array.

Loops a segment of time that is measured from the first keyframe on the layer forward toward the Out point of the layer. The loop plays from the In point of the layer. The segment to loop is determined by the specified duration. The duration value sets the number of composition seconds in a segment to loop; the specified range is measured from the first keyframe. For example, loopInDuration("cycle",1) loops the first second of the entire animation. The default of 0 means that the segment to loop begins at the layer Out point. See the entry for loopIn for more information.

loopOutDuration(type="cycle", duration=0)
Return type: Number or Array.

Loops a segment of time that is measured from the last keyframe on the layer back toward the In point of the layer. The loop plays until the Out point of the layer. The segment to loop is determined by the specified duration. The duration value sets the number of composition seconds in a segment to loop; the specified range is measured backward from the last keyframe. For example, loopOutDuration("cycle", 1) loops the last second of the entire animation. The default of 0 means that the segment to loop begins at the layer In point. See the entry for loopIn for more information.

key(index)
Return type: Key or MarkerKey.

Argument type: index is a Number.

Returns the Key or MarkerKey object by number. For example, key(1) returns the first keyframe.

key(markerName)
Return type: MarkerKey.

Argument type: markerName is a String.

Returns the MarkerKey object with this name. Use only on marker properties.

nearestKey(t)
Return type: Key or MarkerKey.

Returns the Key or MarkerKey object nearest to a designated time.

numKeys
Return type: Number.

Returns the number of keyframes on a property. Returns the number of markers on a marker property.

Note: If you use the Separate Dimensions command to separate the dimensions of the Position property into individual components, the number of keyframes changes, so the value returned by this method changes.

propertyGroup(countUp = 1)
Return type: Group.

Returns a group of properties relative to the property on which the expression is written. For example, if you add the propertyGroup(1) expression to the Rotation property of a brush stroke, the expression targets the Transform property group, which contains the Rotation property. If you add propertyGroup(2) instead, the expression targets the Brush property group. This method lets you establish name-independent relationships in the property hierarchy. This method is especially useful when duplicating properties that contain expressions.

The numProperties method for propertyGroup returns the number of properties in the property group.

This example returns the number of properties in the group that contains the property on which the expression is written:

  thisProperty.propertyGroup(1).numProperties

propertyIndex
Return type: Number.

Returns the index of a property relative to other properties in its property group, including property groups within masks, effects, text animators, selectors, shapes, trackers, and track points.

name
Return type: String.

Returns the name of the property or property group.

Example: Animating with the propertyGroup method and propertyIndex attribute

Values of propertyGroup relative to Position property of a brush stroke

A.
propertyGroup(4)

B.
propertyGroup(3)

C.
propertyGroup(2)

D.
propertyGroup(1)

E.
Position propertyIndex value is 2; Rotation propertyIndex value is 4.

In this example, the propertyGroup method for each brush stroke targets the Brush property group because that group is two property groups up from the Rotation property. The propertyIndex attribute in each Brush stroke then returns a unique value for each Brush stroke. The resulting value is then multiplied by the time and 200 and applied to each rotation value, rotating each brush stroke differently, creating swirling paint strokes:
  propertyGroup(2).propertyIndex * time * 200
Animating a brush stroke with an expression