Use the After Effects expression elements along with standard JavaScript elements to write your expressions. You can use the Expression Language menu at any time to insert methods and attributes into an expression, and you can use the pick whip at any time to insert properties.

If an argument description contains an equal sign (=) and a value (such as t=time or width=.2), then the argument uses the included default value if you don’t specify a different value.

Some argument descriptions include a number in square brackets—this number indicates the dimension of the expected property or Array.

Some return-value descriptions include a number in square brackets—this number specifies the dimension of the returned property or Array. If a specific dimension is not included, the dimension of the returned Array depends on the dimension of the input.

The W3Schools JavaScript reference website provides information for the standard JavaScript language, including pages for the JavaScript Math and String objects.

comp(name)

Return type: Comp.

Argument type: *name* is
a String.

Retrieves another composition by name.

footage(name)

Return type: Footage.

Argument type: *name* is
a String.

Retrieves a footage item by name.

thisLayer

Return type: Layer, Light, or Camera.

Represents the layer containing the expression. Because thisLayer is the default object, its use is optional. For example, you can start an expression with thisLayer.width or width and get the same result.

thisProperty

Return type: Property.

Represents the property containing the expression. For example, if you write an expression on the Rotation property, you can start an expression with thisProperty to refer to the Rotation property.

time

Return type: Number.

Represents the composition time, in seconds, at which the expression is being evaluated.

colorDepth

Return type: Number.

Returns the project color depth value. For example, colorDepth returns 16 when the project color depth is 16 bits per channel.

posterizeTime(framesPerSecond)

Return type: Number.

Argument type: *framesPerSecond* is
a Number.

The *framesPerSecond* value becomes
the frame rate from which the rest of the expression operates. This
expression allows you to set the frame rate for a property to be
lower than the frame rate of the composition. For example, the following
expression updates the property value with a random value once per second:

value

Return type: Number, Array, or String.

Represents the value at the current time for the property containing the expression.

timeToFrames(t = time + thisComp.displayStartTime, fps = 1.0 / thisComp.frameDuration, isDuration = false)

Return type: Number.

Argument type: *t* and *fps* are
Numbers; *isDuration* is a Boolean.

Converts
the value of *t*, which defaults to the current
composition time, to an integer number of frames. The number of
frames per second is specified in the *fps* argument,
which defaults to the frame rate of the current composition (1.0 / thisComp.frameDuration).
The *isDuration* argument, which defaults to false,
should be true if the *t* value represents a difference
between two times instead of an absolute time. Absolute times are
rounded down toward negative infinity; durations are rounded away
from zero (up for positive values).

framesToTime(frames, fps = 1.0 / thisComp.frameDuration)

Return type: Number.

Argument type: *frames* and *fps* are
Numbers.

The inverse of timeToFrames. Returns
the time corresponding to the *frames* argument,
which is required. It doesn’t have to be an integer. See timeToFrames for
explanation of the *fps* argument.

timeToTimecode(t = time + thisComp.displayStartTime, timecodeBase = 30, isDuration = false)

Return type: String.

Argument type: *t* and *timecodeBase* are
Numbers; *isDuration* is a Boolean.

Converts
the value of *t* to a String representing timecode.
See timeToFrames for an explanation of the *t* and *isDuration* arguments.
The *timecodeBase* value, which defaults to 30,
specifies the number of frames in one second.

timeToNTSCTimecode(t = time + thisComp.displayStartTime, ntscDropFrame = false, isDuration = false)

Return type: String.

Argument type: *t* is
a Number, *ntscDropFrame* and *isDuration* are
Booleans.

Converts *t* to a String representing
NTSC timecode. See timeToFrames for an explanation
of the *t* and *isDuration* arguments.
If *ntscDropFrame* is false (the default), the
result String is NTSC non-drop-frame timecode. If *ntscDropFrame* is true,
the result String is NTSC drop-frame timecode.

timeToFeetAndFrames(t = time + thisComp.displayStartTime, fps = 1.0 / thisComp.frameDuration, framesPerFoot = 16, isDuration = false)

Return type: String.

Argument type: *t*, *fps*,
and *framesPerFoot* are Numbers; *isDuration* is
a Boolean.

Converts the value of *t* to
a String representing feet of film and frames. See timeToFrames for
an explanation of the *t*, *fps*,
and *isDuration* arguments. The *framesPerFoot* argument
specifies the number of frames in one foot of film. It defaults
to 16, which is the most common rate for 35mm footage.

timeToCurrentFormat(t = time + thisComp.displayStartTime, fps = 1.0 / thisComp.frameDuration, isDuration = false)

Return type: String.

Argument type: *t* and *fps* are Numbers; *isDuration* is a Boolean.

Converts the value of *t* to a String representing time in the current Project Settings display format. See timeToFrames for a definition of all the arguments.

An optional ntscDropFrame argument was added to the timeToCurrentFormat() function in After Effects CS5.5 and later. Default: ntscDropFrame = thisComp.ntscDropFrame.

Note:

If you want more control over the look of timecode in your footage, use the timeToCurrentFormat method or other timeTo methods to generate the timecode instead of using the Timecode or Numbers effect. Create a text layer, add an expression to the Source Text property, and enter timeToCurrentFormat() in the expression field. With this method, you can format and animate the timecode text. In addition, the timecode uses the same display style defined by the current project settings.

Vector Math functions are global methods that perform operations on arrays, treating them as mathematical vectors. Unlike built-in JavaScript methods, such as Math.sin, these methods are not used with the Math prefix. Unless otherwise specified, Vector Math methods are lenient about dimensions and return a value that is the dimension of the largest input Array object, filling in missing elements with zeros. For example, the expression add([10, 20], [1, 2, 3]) returns [11, 22, 3].

JJ Gifford’s website provides explanations and examples that show how to use simple geometry and trigonometry with expressions.

mul(vec, amount)

Return type: Array.

Argument type: *vec* is
an Array, *amount* is a Number.

Multiplies every element of the vector by the amount.

div(vec, amount)

Return type: Array.

Argument type: *vec* is
an Array, *amount* is a Number.

Divides every element of the vector by the amount.

clamp(value, limit1, limit2)

Return type: Number or Array.

Argument type: *value*, *limit1*, and *limit2* are Numbers or Arrays.

The value of each component of *value* is constrained to fall between the values of the corresponding values of *limit1* and *limit2*.

dot(vec1, vec2)

Return type: Number.

Argument type: *vec1* and *vec2* are
Arrays.

Returns the dot (inner) product of the vector arguments.

cross(vec1, vec2)

Return type: Array [2 or 3].

Argument type: *vec1* and *vec2* are
Arrays [2 or 3].

Returns the vector cross product of *vec1* and *vec2*.
Refer to a math reference or JavaScript guide for more information.

normalize(vec)

Return type: Array.

Argument type: *vec* is
an Array.

Normalizes the vector so that its length is 1.0. Using the normalize method is a short way of performing the operation div(vec, length(vec)).

length(point1, point2)

Return type: Number.

Argument type: *point1* and *point2* are
Arrays.

Returns the distance between two points. The *point2* argument
is optional. For example, length(point1, point2) is
the same as length(sub(point1, point2)).

For example, add this expression to the Focus Distance property of a camera to lock the focal plane to the camera's point of interest so that the point of interest is in focus:

length(position, pointOfInterest)lookAt(fromPoint, atPoint)

Return type: Array [3].

Argument type: *fromPoint* and *atPoint* are Arrays [3].

The argument *fromPoint* is the location in world space of the layer you want to orient. The argument *atPoint* is the point in world space you want to point the layer at. The return value can be used as an expression for the Orientation property, making the z-axis of the layer point at *atPoint*. This method is especially useful for cameras and lights. If you use this expression on a camera, turn off auto-orientation. For example, this expression on the Orientation property of a spot light makes the light point at the anchor point of layer number 1 in the same composition: lookAt(position, thisComp.layer(1).position)

Note:

The wiggle method—which is used to randomly vary a property value—is in the Property attributes and methods category. (See Property attributes and methods (expression reference).)

seedRandom(offset, timeless=false)

Return type: none.

Argument type: *offset* is
a Number,* timeless* is a Boolean.

The random and gaussRandom methods use a seed value that controls the sequence of numbers. By default, the seed is computed as a function of a unique layer identifier, the property within the layer, the current time, and an offset value of 0. Call seedRandom to set the offset to something other than 0 to create a different random sequence.

Use true for
the *timeless* argument to not use the current
time as input to the random seed. Using true for
the *timeless* argument allows you to generate
a random number that doesn’t vary depending on the time of evaluation.

The *offset* value,
but not the *timeless* value, is also used to control
the initial value of the wiggle function.

For example, this expression on the Opacity property sets the Opacity value to a random value that does not vary with time:

seedRandom(123456, true); random()*100The multiplication by 100 in this example converts the value in the range 0–1 returned by the random method into a number in the range 0–100; this range is more typically useful for the Opacity property, which has values from 0% to 100%.

random()

Return type: Number.

Returns a random number in the range 0–1.

In After Effects CC and CS6, the behavior of random() is changed to be more random when layer IDs are close together. The wiggle() expression is not affected.

random(maxValOrArray)

Return type: Number or Array.

Argument type: *maxValOrArray* is
a Number or Array.

If *maxValOrArray* is
a Number, this method returns a number in the range from 0 to *maxValOrArray*.
If *maxValOrArray* is an Array, this method returns
an Array with the same dimension as* maxValOrArray,* with
each component ranging from 0 to the corresponding component of* maxValOrArray.*

random(minValOrArray, maxValOrArray)

Return type: Number or Array.

Argument type: *minValOrArray* and *maxValOrArray* are
Numbers or Arrays.

If *minValOrArray* and *maxValOrArray* are
Numbers, this method returns a number in the range from *minValOrArray* to *maxValOrArray*.
If the arguments are Arrays, this method returns an Array with the
same dimension as the argument with the greater dimension, with
each component in the range from the corresponding component of *minValOrArray* to
the corresponding component of *maxValOrArray*.
For example, the expression random([100, 200], [300, 400]) returns
an Array whose first value is in the range 100–300 and whose second value
is in the range 200–400. If the dimensions of the two input Arrays
don’t match, higher-dimension values of the shorter Array are filled
out with zeros.

gaussRandom()

Return type: Number.

Returns a random number. The results have a Gaussian (bell-shaped) distribution. Approximately 90% of the results are in the range 0–1, and the remaining 10% are outside this range.

gaussRandom(maxValOrArray)

Return type: Number or Array.

Argument type: *maxValOrArray* is
a Number or Array.

When *maxValOrArray* is
a Number, this method returns a random number. Approximately 90%
of the results are in the 0 to *maxValOrArray* range,
and the remaining 10% are outside this range. When *maxValOrArray* is
an Array, this method returns an Array of random values, with the
same dimension as *maxValOrArray*. 90% of the values
are in the range from 0 to *maxValOrArray*, and
the remaining 10% are outside this range. The results have a Gaussian
(bell-shaped) distribution.

gaussRandom(minValOrArray, maxValOrArray)

Return type: Number or Array.

Argument type: *minValOrArray* and *maxValOrArray* are
Numbers or Arrays.

If *minValOrArray* and *maxValOrArray* are
Numbers, this method returns a random number. Approximately 90%
of the results are in the range from *minValOrArray* to *maxValOrArray*,
and the remaining 10% are outside this range. If the arguments are
Arrays, this method returns an Array of random numbers with the same
dimension as the argument with the greater dimension. For each component,
approximately 90% of the results are in the range from the corresponding
component of *minValOrArray* to the corresponding
component of *maxValOrArray*, and the remaining
10% are outside this range. The results have a Gaussian (bell-shaped)
distribution.

noise(valOrArray)

Return type: Number.

Argument type: *valOrArray* is a Number or an Array [2 or 3].

Returns a number in the range from -1 to 1. The noise is not actually random; it is based on Perlin noise, which means that the return values for two input values that are near one another tend to be near one another. This type of noise is useful when you want a sequence of seemingly random numbers that don’t vary wildly from one to the other—as is usually the case when animating any apparently random natural motion. Example: rotation + 360*noise(time)

For all the Interpolation methods, the argument *t* is often time or value, though it can have other values, instead. If *t* is time, the interpolation between values happens over a duration. If *t* is value, then the expression maps one range of values to a new range of values.

For additional explanations and examples of the Interpolation methods, see JJ Gifford’s website.

Chris and Trish Meyer provide additional information and examples for these methods in an article on the ProVideo Coalition website.

Ian Haigh provides a script on After Effects Scripts website that you can use to easily apply advanced interpolation method expressions—such as bounces—to properties.

Andrew Devis provides a pair of video tutorials on the Creative COW website that show in detail how to use the linear expression method along with the Convert Audio To Keyframes command.

linear(t, tMin, tMax, value1, value2)

Return type: Number or Array.

Argument type: *t*, *tMin*, and *tMax* are Numbers, and *value1* and *value2* are Numbers or Arrays.

Returns *value1* when *t* <= *tMin*. Returns *value2* when *t* >= *tMax*. Returns a linear interpolation between *value1* and *value2* when *tMin* < *t* < *tMax*.

For example, this expression on the Opacity property causes Opacity values to ramp linearly from 20% to 80% over the time from 0 seconds to 6 seconds:

linear(time, 0, 6, 20, 80)

This method—like all the Interpolation methods—can also be used to convert from one range of values to another. For example, this expression on the Opacity property converts the Opacity values from the range 0%-100% to the range 20%-80%:

linear(value, 0, 100, 20, 80)

linear(t, value1, value2)

Return type: Number or Array.

Argument type: *t* is
a Number, and *value1* and *value2* are
Numbers or Arrays.

Returns a value that linearly interpolates
from *value1* to *value2* as *t* ranges
from 0 to 1. Returns *value1* when *t* <=
0. Returns *value2* when *t* >=
1.

ease(t, value1, value2)

Return type: Number or Array.

Argument type: *t* is a Number, and *value1* and *value2* are Numbers or Arrays.

Similar to linear with the same arguments, except that the interpolation eases in and out so that the velocity is 0 at the start and end points. This method results in a smooth animation.

ease(t, tMin, tMax, value1, value2)

Return type: Number or Array.

Argument type: *t*, *tMin*, and *tMax* are Numbers, and *value1* and *value2* are Numbers or Arrays.

Similar to linear with the same arguments, except that the interpolation eases in and out so that the velocity is 0 at the start and end points. This method results in a smooth animation.

easeIn(t, value1, value2)

Return type: Number or Array.

Argument type: *t* is
a Number, and *value1* and *value2* are
Numbers or Arrays.

Similar to ease, except
that the tangent is 0 only on the *value1* side
and interpolation is linear on the *value2* side.

easeIn(t, tMin, tMax, value1, value2)

Return type: Number or Array.

Argument type: *t*, *tMin*,
and *tMax* are Numbers, and *value1* and *value2* are Numbers
or Arrays.

Similar to ease, except that
the tangent is 0 only on the *tMin* side and interpolation
is linear on the *tMax* side.

easeOut(t, value1, value2)

Return type: Number or Array.

Argument type: *t* is
a Number, and *value1* and *value2* are
Numbers or Arrays.

Similar to ease, except
that the tangent is 0 only on the *value2* side
and interpolation is linear on the *value1* side.

easeOut(t, tMin, tMax, value1, value2)

Return type: Number or Array.

Argument type: *t*, *tMin*,
and *tMax* are Numbers, and *value1* and *value2* are Numbers
or Arrays.

Similar to ease, except that
the tangent is 0 only on the *tMax* side and interpolation
is linear on the *tMin* side.

Harry Frank provides a video tutorial on his graymachine website that shows how to use these color conversion methods to change the color of the waves produced by the Radio Waves effect.

rgbToHsl(rgbaArray)

Return type: Array [4].

Argument type: *rgbaArray* is
an Array [4].

Converts a color in RGBA space to HSLA space. The input is an Array of normalized red, green, blue, and alpha channel values, all in the range of 0.0 to 1.0. The resulting value is an Array of hue, saturation, lightness, and alpha channel values, also in the range of 0.0 to 1.0. Example:

rgbToHsl.effect("Change Color")("Color To Change")hslToRgb(hslaArray)

Return type: Array [4].

Argument type: *hslaArray* is
an Array [4].

Converts a color in HSLA space to RGBA space. This conversion is the opposite of the conversion performed by the rgbToHsl method.

degreesToRadians(degrees)

Return type: Number.

Argument type: *degrees* is
a Number.

Converts degrees to radians.

radiansToDegrees(radians)

Return type: Number.

Argument type: *radians* is
a Number.

Converts radians to degrees.

layer(index)

Return type: Layer, Light, or Camera.

Argument type: *index* is
a Number.

Retrieves the layer by number (order in the Timeline panel). Example: thisComp.layer(3)

layer(name)

Return type: Layer, Light, or Camera.

Argument type: *name* is
a String.

Retrieves the layer by name. Names are matched according to layer name, or source name if there is no layer name. If duplicate names exist, After Effects uses the first (topmost) one in the Timeline panel. Example:

thisComp.layer("Solid 1")layer(otherLayer, relIndex)

Return type: Layer, Light, or Camera.

Argument type: *otherLayer* is
a Layer object, and *relIndex* is a Number.

Retrieves
the layer that is *relIndex* layers above or below *otherLayer*.
For example, thisComp.layer(thisLayer, 1).active returns
true if the next layer down in the Timeline panel is active.

Note:

You cannot access a composition marker by marker number. If you have a project created in a previous version of After Effects that uses composition marker numbers in expressions, you must change those calls to use marker.key(name) instead. Because the default name of a composition marker is a number, converting the reference to use the name is often just a matter of surrounding the number with quotation marks.

marker.key(index)

Return type: MarkerKey.

Argument type: *index* is a Number.

Returns the MarkerKey object of the marker with the specified index. The index refers to the order of the marker in composition time, not to the name of the marker. For example, this expression returns the time of the first composition marker:

thisComp.marker.key(1).time

marker.key(name)

Return type: MarkerKey.

Argument type: *name* is
a String.

Returns the MarkerKey object of the marker with
the specified name. The *name* value is the name
of the marker, as typed in the comment field in the marker dialog
box, for example, marker.key("1"). For a composition
marker, the default name is a number. If more than one marker in
the composition has the same name, this method returns the marker
that occurs first in time (in composition time). The value for a
marker key is a String, not a Number. For example, this expression
returns the time of the composition marker with the name "0":

marker.nearestKey(t)

Return type: MarkerKey.

Argument type: *t* is
a Number.

Returns the marker that is nearest in time to *t*.
For example, this expression returns the time of the composition
marker nearest to the time of 1 second:

This expression returns the time of the composition marker nearest to the current time:

thisComp.marker.nearestKey(time).timemarker.numKeys

Return type: Number.

Returns the total number of composition markers in the composition.

activeCamera

Return type: Camera.

Returns the Camera object for the camera through which the composition is rendered at the current frame. This camera is not necessarily the camera through which you are looking in the Composition panel.

width

Return type: Number.

Returns the composition width, in pixels.

Apply the following expression to the Position property of a layer to center the layer in the composition frame:

[thisComp.width/2, thisComp.height/2]ntscDropFrame

Return type: Boolean.

Returns true if the timecode is in drop-frame format. (After Effects CS5.5and later.)

To use a footage item from the Project panel as an object in an expression, use the global footage method, as in footage("file_name"). You can also access a footage object using the source attribute on a layer whose source is a footage item.

ntscDropFrame

Return type: Boolean.

Returns true if the timecode is in drop-frame format. (After Effects CS5.5 and later.)

Note:

For After Effects CC and CS6, the Expression language menu, the "Layer Sub-objects", "Layer General", "Layer Properties", "Layer 3D", and "Layer Space Transforms" have been arranged into a "Layer" submenu.

source

Return type: Comp or Footage.

Returns the source Comp or source Footage object for the layer. Default time is adjusted to the time in the source. Example: source.layer(1).position

sourceTime(t = time)

Return type: Number.

Returns the layer source corresponding to time t. (After Effects CS5.5 and later.)

effect(name)

Return type: Effect.

Argument type: *name* is
a String.

After Effects finds the effect by its name in the Effect Controls panel. The name can be the default name or a user-defined name. If multiple effects have the same name, the effect closest to the top of the Effect Controls panel is used. Example:

effect("Fast Blur")("Blurriness")effect(index)

Return type: Effect.

Argument type: *index* is
a Number.

After Effects finds the effect by its index in the Effect Controls panel, starting at 1 and counting from the top.

mask(name)

Return type: Mask.

Argument type: *name* is
a String.

The name can be the default name or a user-defined name. If multiple masks have the same name, the first (topmost) mask is used. Example:

mask("Mask 1")mask(index)

Return type: Mask.

Argument type: *index* is
a Number.

After Effects finds the mask by its index in the Timeline panel, starting at 1 and counting from the top.

width

Return type: Number.

Returns the width of the layer, in pixels. It is the same as source.width.

height

Return type: Number.

Returns the height of the layer, in pixels. It is the same as source.height.

parent

Return type: Layer, Light, or Camera.

Returns the parent Layer object of the layer, if it has one. Example: position[0] + parent.width

hasParent

Return type: Boolean.

Returns true if the layer has a parent or false if it doesn’t.

Use the hasParent attribute to determine if a layer has a parent layer. You can use this attribute even if the layer has no parent layer at present. For example, the following expression indicates that the layer to which you apply it wiggles based on the position of the parent. If the layer has no parent, then it wiggles based on its own position. If the layer is given a parent later, then the behavior of the layer changes accordingly:

idx = index; if (hasParent) { idx = parent.index; } thisComp.layer(idx).position.wiggle(5,20)Note:

In general, the value of outPoint is greater than the value of inPoint. However, if a layer is reversed in time, the value of inPoint is greater than the value of outPoint. Similarly, the value of startTime can be greater than the value of inPoint.

active

Return type: Boolean.

Returns true if the Video switch is on for the layer and the current time is in the range from the In point of the layer to the Out point of the layer; false otherwise.

audioActive

Return type: Boolean.

Returns true if the Audio switch is on for the layer and the current time is in the range from the In point of the layer to the Out point of the layer; false otherwise.

sampleImage(point, radius = [.5, .5], postEffect=true, t=time)

Return type: Array [4].

Argument type: *point* is an Array [2], *radius* is an Array [2], *postEffect* is a Boolean, and *t* is a Number.

Samples the color and alpha channel values of a layer and returns the average alpha-weighted value of the pixels within the specified distance of the point as an array: [*red*, *green*, *blue*, *alpha*]. If *postEffect* is true, the sampled values are for the layer after masks and effects on that layer have been rendered; if *postEffect* is false, the sampled values are for the layer before masks and effects have been rendered. The input value *point* is in layer space; the point [0,0] is the center of the upper-left pixel in the layer. The input value *radius* specifies the horizontal and vertical distance from the sample center to the edges of the sampled rectangle. The default value samples one pixel.

Note:

The postEffect parameter refers to effects applied directly to the layer, not to effects applied indirectly, such as with an adjustment layer.

Note:

Using sampleImage in an expression no longer disables multiprocessing.

This example samples a rectangle 4 pixels wide and 3 pixels high, centered around a point 100 pixels down and to the right of the upper-left corner of the layer:

thisComp.layer(1).sampleImage([100, 100], [2, 1.5])

Dan Ebberts provides an example of how to use the sampleImage method on his MotionScript website.

Todd Kopriva provides instructions for using the sampleImage method and the Point Control effect to monitor colors for a specified point during color correction on his After Effects Region of Interest blog.

When you add masks, effects, paint, or text to a layer, After Effects adds new properties to the Timeline panel. There are too many of these properties to list here, so use the pick whip to learn the syntax for referring to them in your expressions.

anchorPoint

Return type: Property [2 or 3].

Returns the anchor point value of the layer in the coordinate system of the layer (layer space).

position

Return type: Property [2 or 3].

Returns the position value of the layer, in world space if the layer has no parent. If the layer has a parent, it returns the position value of the layer in the coordinate system of the parent layer (in the layer space of the parent layer).

scale

Return type: Property [2 or 3].

Returns the scale value of the layer, expressed as a percentage.

rotation

Return type: Property.

Returns the rotation value of the layer in degrees. For a 3D layer, it returns the z rotation value in degrees.

audioLevels

Return type: Property [2].

Returns the value of the Audio Levels property of the layer, in decibels. This value is a 2D value; the first value represents the left audio channel, and the second value represents the right. The value is not the amplitude of the audio track of the source material. Instead, it is the value of the Audio Levels property, which may be affected by keyframes.

timeRemap

Return type: Property.

Returns the value of the Time Remap property, in seconds, if Time Remap is enabled.

marker.key(index)

Return type: MarkerKey.

Argument type: *index* is
a Number.

Returns the MarkerKey object of the layer marker with the specified index.

marker.key(name)

Return type: MarkerKey.

Argument type: *name* is
a String.

Returns the MarkerKey object of the layer marker
with the specified name. The *name* value is the
name of the marker, as typed in the comment field in the marker
dialog box, for example, marker.key("ch1"). If
more than one marker on the layer has the same name, this method
returns the marker that occurs first in time (in layer time). The
value for a marker key is a String, not a Number.

This expression on a property ramps the value of the property from 0 to 100 between two markers identified by name:

m1 = marker.key("Start").time; m2 = marker.key("End").time; linear(time, m1, m2, 0, 100);marker.nearestKey(t)

Return type: MarkerKey.

Argument type: *t* is
a Number.

Returns the layer marker that is nearest in time
to *t*. For example, this expression returns the
time of the marker on the layer nearest to the time of 1 second:

This expression returns the time of the marker on the layer nearest to the current time:

marker.nearestKey(time).timelightTransmission

Return type: Property.

Returns the value of the Light Transmission property for a 3D layer.

Use layer space transform methods to transform values from one space to another, such as from layer space to world space. The “from” methods transform values from the named space (composition or world) to the layer space. The “to” methods transform values from the layer space to the named space (composition or world). Each transform method takes an optional argument to determine the time at which the transform is computed; however, you can almost always use the current (default) time.

Use “Vec” transform methods when transforming a direction vector, such as the difference between two position values. Use the plain (non-”Vec”) transform methods when transforming a point, such as position. Composition (comp) and world space are the same for 2D layers. For 3D layers, however, composition space is relative to the active camera, and world space is independent of the camera.

toComp(point, t=time)

Return type: Array [2 or 3].

Argument type: *point* is
an Array [2 or 3], and *t *is a Number.

Transforms a point from layer space to composition space.

fromComp(point, t=time)

Return type: Array [2 or 3].

Argument type: *point* is
an Array [2 or 3], and *t* is a Number.

Transforms a point from composition space to layer space. The resulting point in a 3D layer may have a nonzero value even though it is in layer space. Example: fromComp(thisComp.layer(2).position)

toWorld(point, t=time)

Return type: Array [2 or 3].

Argument type: *point* is an Array [2 or 3], and *t* is a Number.

Transforms a point from layer space to view-independent world space. Example:

toWorld.effect("Bulge")("Bulge Center")

Dan Ebberts provides an expression on his MotionScript website that uses the toWorld method to auto-orient a layer along only one axis. This is useful, for example, for having characters turn from side to side to follow the camera while remaining upright.

Rich Young provides a set of expressions on his AE Portal website that use the toWorld method link a camera and light to a layer with the CC Sphere effect.

fromWorld(point, t=time)

Return type: Array [2 or 3].

Argument type: *point* is
an Array [2 or 3], and *t* is a Number.

Transforms a point from world space to layer space. Example: fromWorld(thisComp.layer(2).position)

See Expression example: Create a bulge between two layers for an example of how this method can be used.

toCompVec(vec, t=time)

Return type: Array [2 or 3].

Argument type: *vec* is
an Array [2 or 3], and *t* is a Number.

Transforms a vector from layer space to composition space. Example: toCompVec([1,0])

fromCompVec(vec, t=time)

Return type: Array [2 or 3].

Argument type: *vec* is
an Array [2 or 3], and *t* is a Number.

Transforms a vector from composition space to layer space. Example (2D layer):

dir=sub(position, thisComp.layer(2).position); fromCompVec(dir)toWorldVec(vec, t=time)

Return type: Array [2 or 3].

Argument type: *vec* is
an Array [2 or 3], and *t* is a Number.

Transforms a vector from layer space to world space. Example: p1 = effect("Eye Bulge 1")("Bulge Center"); p2 = effect("Eye Bulge 2")("Bulge Center"); toWorld(sub(p1, p2))

fromWorldVec(vec, t=time)

Return type: Array [2 or 3].

Argument type: *vec* is
an Array [2 or 3], and *t* is a Number.

Transforms a vector from world space to layer space. Example: fromWorld(thisComp.layer(2).position)

fromCompToSurface(point, t=time)

Return type: Array [2].

Argument type: *point* is
an Array [2 or 3], and *t* is a Number.

Projects a point located in composition space to a point on the surface of the layer (zero z-value) at the location where it appears when viewed from the active camera. This method is useful for setting effect control points. Use with 3D layers only.

Camera objects have the same attributes and methods as Layer objects, except for source, effect, mask, width, height, anchorPoint, scale, opacity, audioLevels, timeRemap, and all the material properties.

pointOfInterest

Return type: Property [3].

Returns the point of interest values of a camera in world space.

zoom

Return type: Property.

Returns the zoom values of a camera in pixels.

Here’s an expression for the Scale property of a layer that maintains the relative size of the layer in frame while changing the z position (depth) of a layer or the Zoom value of a camera:

cam = thisComp.activeCamera; distance = length(sub(position, cam.position)); scale * distance / cam.zoom;depthOfField

Return type: Property.

Returns 1 if the Depth Of Field property of a camera is on, or returns 0 if the Depth Of Field property is off.

active

Return type: Boolean.

Returns true if the camera is the active camera for the composition at the current time: the Video switch for the camera layer is on, the current time is in the range from the In point of the camera layer to the Out point of the camera layer, and it is the first (topmost) such camera layer listed in the Timeline panel. Returns false otherwise.

Light objects have the same attributes and methods as Layer objects, except for source, effect, mask, width, height, anchorPoint, scale, opacity, audioLevels, timeRemap, and all the material properties.

pointOfInterest

Return type: Property [3].

Returns the point of interest values for a light in world space.

David Van Brink provides an instructional article and sample project on his omino pixel blog that show how to use expressions with lights.

active

Return type: Boolean.

Returns true if the effect is turned on (the Effect switch is selected).

param(name)

Return type: Property.

Argument type: *name* is
a String.

Returns a property within an effect. Effect control points are always in layer space. Example:

effect("Bulge").param("Bulge Height")param(index)

Return type: Property.

Argument type: *index* is
a Number.

Returns a property within an effect. Effect control points are always in layer space. For example, effect("Bulge").param(4) returns the Bulge Height property.

Note:

You can link Mask Path properties to other path properties (paths in a shape layer and brush strokes), but the properties are not accessible for direct numerical manipulation through expressions.

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]];

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 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 |

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 specified number of keyframes determines the segment to loop. 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 loop. See the entry for loopIn for more information.

David Van Brink provides an instructional article and sample project on his

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. Specified duration determines the segment to loop. 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. Specified duration determines the segmetn to loop. 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).numPropertiespropertyIndex

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.

**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

propertyGroup(2).propertyIndex * time * 200

When you access a Key object, you can get time, index, and value properties from it. For example, the following expression gives you the value of the third Position keyframe: position.key(3).value.

The following expression, when written on an Opacity property with keyframes, ignores the keyframe values and uses only the placement of the keyframes in time to determine where a flash should occur: d = Math.abs(time - nearestKey(time).time); easeOut(d, 0, .1, 100, 0)

d = Math.abs(time - nearestKey(time).time); easeOut(d, 0, .1, 100, 0)

You can access values for composition markers and layer markers using the same methods. Access layer markers through the thisLayer.marker object; access composition markers through the thisComp.marker object.

For the purpose of expressions, markers are a special type of Key object, so you can use methods such as nearestKey(time) to access markers, and markers also have time and index attributes. The index attribute is not the number (name) of the marker; it is the keyframe index number, representing the order of the marker in the time ruler.

Expressions have access to all the values for a marker that you can set in the Composition Marker or Layer Marker dialog box. This expression on the Source Text property of a text layer displays the time, duration, index, comment (name), chapter, URL, frame target, and cue point name for the layer marker nearest the current time, and whether the marker is for an event cue point:

m = thisLayer.marker.nearestKey(time); s = "time:" + timeToCurrentFormat(m.time) + "\r" + "duration: " + m.duration + "\r" + "key index: " + m.index + "\r" + "comment:" + m.comment + "\r" + "chapter:" + m.chapter + "\r" + "URL:" + m.url + "\r" + "frame target: " + m.frameTarget + "\r" + "cue point name: " + m.cuePointName + "\r" + "Event cue point? " + m.eventCuePoint + "\r"; for (param in m.parameters){ s += "parameter: " + param + " value: " + m.parameters[param] + "\r"; } s

Because the XMP metadata in a footage item can be converted into layer markers for a layer based on that item, expressions can interact with XMP metadata. For information, see XMP metadata in After Effects.

Dan Ebberts provides a tutorial on the After Effects Developer Center that includes an example of using XMP metadata with expressions.

eventCuePoint

Return type: Boolean.

Setting for cue point type in marker dialog box. True for Event; false for Navigation.

parameters

Return type: associative array of String values.

Contents of Parameter Name and Parameter Value fields in marker dialog box.

For example, if you have a parameter named “background color”, then you can use the following expression to access its value at the nearest marker:

thisComp.marker.nearestKey(time).parameters["background color"]You can use expressions to read and write the x and y coordinates of path points, or vertices, for:

- Layer masks
- Bezier shapes
- Brush strokes on the Paint and Roto Brush & Refine Edge effects.

Expression methods:

**Path points() method:**{pathProperty}.points(t = time) Get the x,y coordinates of all points on a path. Coordinates for layer mask path points are relative to the layer's origin in its upper-left hand corner. Coordinates for Bezier shape path points are are relative to the anchor point of the path's shape group for example, Transform: Shape 1 > Anchor Point. Coordinates for brush stroke path points are relative to the start of the stroke; the first point is [0,0]. Optionally specify the time at which to sample the path. You can pass this method into the createPath() method for the points parameter when duplicating a path.

**Parameters**:

t | Number, optional. The composition time (in seconds) at which to sample the path. Default is time (the current time). |

**Path inTangents() method: {pathProperty}.inTangents(t = time)**Get the x,y coordinates of the incoming tangent handle for all points on a path. Tangent coordinate values are offset relative to the parent point's coordinates. i.e., The value [0,0] creates no curvature at the incoming tangent. This method can be passed into the createPath() method for the inTangents parameter when duplicating a path. Optionally specify the time at which to sample the path.

**Parameters**:

t | Number, optional. The composition time (in seconds) at which to sample the path. Default is time (the current time). |

**Path outTangents() method: {pathProperty}.outTangents(t = time)**Get the x,y coordinates of the outgoing tangent handle for all points on a path. Tangent coordinate values are offset relative to the parent point's coordinates - The value [0,0] creates no curvature at the outgoing tangent.This method can be passed into the createPath() method for the outTangents parameter when duplicating a path. Optionally specify the time at which to sample the path.

**Parameters**:

t | Number, optional. The composition time (in seconds) at which to sample the path. Default is time (the current time). |

**Path isClosed() method**: {pathProperty}.isClosed()Determines if the path is open or closed. Returns true if the path is closed, false if the path is open. This method can be passed into the createPath() method for the is_closed parameter when duplicating a path.

**Parameters**:

None

**Returns**:

Boolean

**Path pointOnPath() method**{pathProperty}.pointOnPath(percentage = 0.5, t = time)Get the x,y coordinates of an arbitrary point along a path.The point is expressed as a percentage of the arc-length of the path. 0% is the first point and 100% is the last point. When the path is closed, 0% and 100% will return the same coordinates. Percentage of arc-length is used to ensure uniform speed along the path. Other than 0% and 100%, percentages do not necessarily correlate with the Bezier points on the path - For a path with three points, the second point will not necessarily be at 50%.) This also means that for an open path and closed path with identical points, the percentage along the open path will not return the same coordinates as the closed path due to the additional length of the closed path. Optionally specify the time at which to sample the path.

**Parameters**:

percentage | Number between 0 and 1, optional. The percentage along the arc-length of the path to sample. Values smaller than 0 and larger than 1 are clipped. Default is 0.5. |

t |

**Path tangentOnPath() method**{pathProperty}.tangentOnPath(percentage = 0.5, t = time) Get the calculated x,y coordinates of the outgoing tangent handle for an arbitrary point along a path. Tangent coordinate values are offset relative to the parent point's coordinates - The value [0,0] creates no curvature at the outgoing tangent. The incoming tangent handle is the inverse of this value (multiply the x,y coordinates by -1). The tangent's parent point is expressed as a percentage of the arc-length of the path. The coordinates returned by tangentOnPath() are calcuated from it's parent point and will differ from those returned by outTangents() if a user-defined point also exists at that arc-length pecentage. The linear distance between the parent point's coordinates and tangentOnPath() coordinates will always be 1. You can multiply the returned coordinates to create a longer tangent, ex. (myPath.tangentOnPath() * 100). Optionally specify the time at which to sample the path.

**Parameters**:

percentage | Number between 0 and 1, optional. The percentage along the arc-length of the path to sample. Values smaller than 0 and larger than 1 are clipped. Default is 0.5. |

t |

**Path normalOnPath() method**{pathProperty}.normalOnPath(percentage = 0.5, t = time) Get the calculated x,y coordinates of the normal for an arbitrary point along a path.Coordinate values of normals are offset relative to the parent point's coordinates - The value [0,0] is the same as the parent point.The normal's parent point is expressed as a percentage of the arc-length of the path. Read the description of the pointOnPath() method for details about arc-length percentage.The coordinates returned by normalOnPath() are calcuated from its parent point. The linear distance between the parent point's coordinates and normalOnPath() coordinates will always be 1. You can multiply the returned coordinates to create a longer normal, for example, (myPath.normalOnPath() * 100). Optionally specify the time at which to sample the path.

**Parameters**:

percentage | Number between 0 and 1, optional. The percentage along the arc-length of the path to sample. Values smaller than 0 and larger than 1 are clipped. Default is 0.5. |

t |

**Path createPath() method**{pathProperty}.createPath(points = [[0,0], [100,0], [100,100], [0,100]], inTangents = [], outTangents = [], is_closed = true) Creates a path object from a set of points and tangents.The points are defined by an array of number pair arrays representing their x,y coordinates. The array length must be at least 1, and can be of any greater length.The incoming and outgoing tangent handles of the points are defined by an array of number pair arrays representing their x,y offset coordinates. The length of the tangent arrays must be exactly the same as the points paramater. Tangent coordinate values are offset relative to the parent point's coordinates - The value [0,0] creates no curvature at the incoming tangent. The points(), inTangents(), outTangents(), and isClosed() methods of a path can be passed into the points, inTangents, outTangents, and is_closed parameters to duplicate a path.The points and tangents of the same path can be passed into createPath() with modifications to generate a different result. For example, the following expression will remove curves from Mask 1 by not passing the inTangents or outTangents parameters:

myMask = mask("Mask 1").path;

myMask.createPath(myMask.points());

The following example passes the points and tangents of Mask 1 and converts it to an open path by setting is_closed to false:

myMask = mask("Mask 1").path;

myMask.createPath(myMask.points(), myMask.inTangents(), myMask.outTangents(), false);

points | An array of length 1 or greater containing number pair arrays representing the [x,y] coordinates of the path points. Required unless no parameters are passed (i.e., createPath()). Default is [[0,0], [100,0], [100,100], [0,100]]. |

is_closed | Boolean, optional. Determines if the mask is closed. If true, the last point will be connected to the first point. Default is true. |

inTangents | An array containing number pair arrays representing the [x,y] offset coordinates of the outgoing tangent handles to the path points. Required unless no parameters are passed (i.e., createPath()). The array length must be the same as points, or you can pass an empty array ([]), which will assume the same length as points and [0,0] for all tangents. Default is an empty array. |

outTangents | An array containing number pair arrays representing the [x,y] offset coordinates of the incoming tangent handles to the path points. Required unless no parameters are passed (i.e., createPath()). The array length must be the same as points, or you can pass an empty array ([]), which will assume the same length as points and [0,0] for all tangents. Default is an empty array. |

**Examples**:

- Example 1

The example writes the list of point and tangent coordinates from Path 1 of Shape 1 on layer Shape Layer 1, at time=0, into a string. Apply this to the source text property of a text layer for a readout of the coordinates and incoming and outgoing tangents of the shape.

pointsList = "";

sampleTime = 0;

myShape = thisComp.layer("Shape Layer 1").content("Shape 1").content("Path 1").path;

for (i = 0; i < myShape.points(sampleTime).length; i++) {

pointsList += "c: " + myShape.points(sampleTime)[i].toString() + " i: " + myShape.inTangents(sampleTime)[i].toString() + " o: " + myShape.outTangents(sampleTime)[i].toString() + "\n";

}

pointsList;

- Example 2

The example reads the coordinates of the first vertex of Mask 1 on Dark Gray Solid 1 and converts them to composition coordinates. Apply this to a 2D point control of an effect, such as Write-on or CC Particle Systems II, to make the effect trace or track the first point of an animated mask. Duplicate the effect and change the path points index value ([0]) to trace or track the other points of the mask.

myLayer = thisComp.layer("Dark Gray Solid 1");

myLayer.toComp(myLayer.mask("Mask 1").maskPath.points()[0]);

Expression methods:

- Footage sourceText attribute {footageItem}.sourceText Returns the contents of a .JSON file as a string. The eval() method can be used to convert the string to an array of sourceData objects, identical to the results of the sourceData attribute, from which the individual data streams can be referenced as hierarchal attributes of the data. For example:

var myData = eval(footage("sample.json").sourceText);

myData.sampleValue;

**Type:**

String, the contents of the .JSON file; read-only.

**Footage sourceData attribute**{footageItem}.sourceData Returns the data of a .JSON file as an array of sourceData objects. The structure of the .JSON file will determine the size and complexity of the array. Individual data streams can be referenced as hierarchal attributes of the data. For example, given a data stream named Color, the following will return the value of Color from the first data object: footage("sample.json").sourceData[0].Color

Typical use is to assign a .JSON file's sourceData to a variable, and then reference the desired data stream. For example:

var myData = footage("sample.json").sourceData;

myData[0].Color;

**Type**:

An array of sourceData objects; read-only.

**Footage dataValue() method**{footageItem}.dataValue(dataPath) Returns the value of specificed static or dynamic data stream in a .mgJSON file. Accepts a single array value to define the path in the hierarchy to the desired data stream. For example:

footage("sample.mgjson").dataValue([0]) returns data of the first child.

footage("sample.mgjson").dataValue([1][0]) returns data of the first child in the second group.

**Parameters:**

**Returns:**

The value of the data stream.

**Footage dataKeyCount() method**{footageItem}.dataKeyCount(dataPath)Returns the number of samples in a specificed dynamic data stream in a .mgJSON file.Accepts a single array value to define the path in the hierarchy to the desired dynamic data stream.

For example:

- footage("sample.mgjson").dataKeyCount([0]) returns the count of samples for the first child
- footage("sample.mgjson").dataKeyCount([1][0]) returns the count of samples for the second group

**Parameters**:

**Returns**:

The number of samples in the dynamic data stream.

**Footage dataKeyTimes() method**{footageItem}.dataKeyTimes(dataPath, t0 = startTime, t1=endTime)Returns the time in seconds for the samples of a specificed dynamic data stream in a .mgJSON file. Optionally specify the time span from which to return samples. By default the time for all samples between startTime and endTime in the dynamic data stream are returned, as defined by the data stream's samplesTemporalExtent property in the .mgJSON file. Accepts a single array value to define the path in the hierarchy to the desired dynamic data stream.

The following example returns the times of samples between 1 second and 3 seconds for the first child:

footage("sample.mgjson").dataKeyTimes([0], 1, 3)

**Parameters**:

dataPath | Array, required. The path in the hierarchy to a dynamic data stream. |

t0 | Number, optional. The start time, in seconds, of the span from which to return samples. Defaults to startTime. |

t1 |
Number, optional. The end time, in seconds, of the span from which to return samples. Defaults to endTime. |

**Returns**:

Array of numbers representing the sample times.

**Footage dataKeyValues() method**{footageItem}.dataKeyValues(dataPath, t0 = startTime, t1=endTime)Returns the values for the samples of a specificed dynamic data stream in a .mgJSON file. Optionally specify the time span from which to return samples. By default the time for all samples between startTime and endTime in the dynamic data stream are returned, as defined by the data stream's samplesTemporalExtent property in the .mgJSON file. Accepts a single array value to define the path in the hierarchy to the desired dynamic data stream.

For example:

footage("sample.mgjson").dataKeyValues([0], 1, 3) returns the values of samples between 1 second and 3 seconds for the first child.

**Parameters**:

dataPath | Array, required. The path in the hierarchy to a dynamic data stream. |

t0 | Number, optional. The start time, in seconds, of the span from which to return samples. Defaults to startTime. |

t1 |
Number, optional. The end time, in seconds, of the span from which to return samples. Defaults to endTime. |