When you animate spatial properties—including Position, Anchor Point, and effect control point properties—the motion is shown as a motion path. A motion path appears as a sequence of dots, where each dot marks the position of the layer at each frame. A box in the path marks the position of a keyframe.

Motion paths are simply an alternative visual, spatial way of viewing and working with spatial properties and their keyframes, in addition to the ways that you work with properties in the Timeline panel. You can modify a motion path by changing an existing keyframe or adding a keyframe. You can modify the shape of a motion path by changing the spatial interpolation methods for its keyframes. (See About spatial and temporal keyframe interpolation.)

The density of dots between the boxes in a motion path indicates the relative speed of the layer or effect control point. Dots close together indicate a lower speed; dots farther apart indicate a greater speed.

Using the Pen tool or Selection tool to edit keyframes for a spatial property in the Composition or Layer panel is like modifying a Bezier path for a mask or for a shape on a shape layer. (See About paths.)

A motion path is less complex and generally easier to modify when you use fewer keyframes to describe the path. You can use the Smoother to remove extraneous keyframes from a motion path.

Show motion path controls

Position motion paths appear in the Composition panel. Anchor Point and effect control point motion paths appear in the Layer panel.

• To show motion path controls in the Composition panel, choose View > View Options, and select Effect Controls, Keyframes, Motion Paths, and Motion Handles. To see a Position motion path in the Composition panel, the Position property must be selected.
• To show motion path controls in the Layer panel, choose the property or effect from the View menu at the bottom of the Layer panel.
• To specify how many keyframes to show for a motion path, choose Edit > Preferences > Display (Windows) or After Effects > Preferences > Display (Mac OS), and select an option in the Motion Path section.
• To specify the size of Bezier direction handles for motion paths, choose Edit > Preferences > General (Windows) or After Effects > Preferences > General (Mac OS), and edit the Path Point Size value.

Move motion path keyframes

Add a keyframe to a motion path using the Pen tool

Sketch a motion path with Motion Sketch

You can draw a path for the motion of a selected layer using Motion Sketch, which records the position of the layer and the speed at which you draw. As you draw, a Position keyframe is generated at each frame.

Motion Sketch does not affect keyframes that you have set for other properties. For example, if you set Rotation keyframes for an image of a ball, you can use Motion Sketch to generate Position keyframes, so that the ball appears to roll along the path you created.

John Dickinson provides a demonstration of Motion Sketch in a video tutorial on his Motionworks website.

Create a motion path from a mask, shape, or paint path

You can create a motion path from any of several types of paths:

• A Mask Path property

• A shape Path property on a shape layer

• A Path property for a paint stroke

• A path copied from Illustrator or Photoshop

You can paste any of these paths into the Position or Anchor Point property for a layer, or into the position property of an effect control point. The pasted keyframes are set to rove in time, except for the first and last ones, to create a constant velocity along the path.

By default, the duration of the pasted motion path is 2 seconds. You can adjust the duration by dragging the first or last keyframe in the Timeline panel.

Andrew Devis shows how to use paths from Illustrator as motion paths in After Effects in this video on the Creative COW website.

Motion blur

When you view one frame of motion-picture film or video containing a moving object, the image is often blurred, because a frame represents a sample of time (in film, a frame is 1/24 of a second long). In that time, a moving object occupies more than one position as it travels across the frame, so it doesn’t appear as a sharp, still object. The faster the object moves, the more it is blurred. The camera shutter angle and shutter phase also affect the appearance of the blur, determining how long the shutter stays open and when the shutter opens relative to the beginning of the frame.

In contrast, in a single frame of a computer-generated animation, you may not be able to tell which objects are moving because all moving objects may appear as sharp and clear as nonmoving objects. Without motion blur, layer animation produces a strobe-like effect of distinct steps instead of an appearance of continuous change. Adding motion blur to layers that you animate in After Effects makes motion appear smoother and more natural.

You enable motion blur for each layer individually, and you also determine whether the motion blur is rendered for previews and final output. Use the Enable Motion Blur composition switch at the top of the Timeline panel to enable or disable motion blur rendering for previews. Modify the render settings in the Render Queue panel to enable or disable motion blur rendering for final output. If the Switches Affect Nested Comps preference in the General preferences category is enabled, then nested compositions obey the setting for the compositions in which they’re contained. (See About precomposing and nesting.)

Motion blur slows rendering, so you may want to disable the composition switch while working, and only enable it to see the finished result.

To enable motion blur for a layer, do one of the following:

• Click the Motion Blur layer switch for the layer in the Timeline panel.
• Select the layer and choose Layer > Switches > Motion Blur.

The number of samples that After Effects uses to calculate motion blur adapts for each layer, depending on the motion of that layer. This adaptivity provides high-quality motion blur without unnecessarily sampling the motion of a slow-moving layer as frequently as the motion of a fast-moving layer. High sampling rates decrease rendering performance.

When motion blur is enabled for a composition and the Timeline panel is zoomed in so that you can see individual frames, a light gray region around the current-time indicator indicates the shutter phase and shutter angle. The width of the column shows the shutter angle, and the offset of the column shows the shutter phase. This visual indication shows how individual frames are sampled to calculate motion blur within this composition.

You can use motion blur when you animate a layer—for example, moving a layer of text across the screen. You cannot add motion blur to motion that exists within a layer by means of the Motion Blur layer switch and Enable Motion Blur composition switch.

If you want to smooth live-action video to which you assigned a frame rate much lower or higher than the original, use frame blending, not motion blur.

To create a fake motion blur, see Apply motion blur.

Motion blur settings in the Advanced tab of Composition Settings

The minimum number of samples. This minimum is the number of samples used for frames for which After Effects is not able to determine an adaptive sampling rate based on layer motion. This sample rate is used for 3D layers and shape layers.

The maximum number of samples.

The shutter angle is measured in degrees, simulating the exposure allowed by a rotating shutter. The shutter angle uses the footage frame rate to determine the simulated exposure, which affects the amount of motion blur. For example, entering 90° (25% of 360°) for 24-fps footage creates an effective exposure of 1/96 of a second (25% of 1/24 of a second). Entering 1° applies almost no motion blur, and entering 720° applies a large amount of blur.

The shutter phase is also measured in degrees. It defines an offset that determines when the shutter opens relative to the beginning of a frame. Adjusting this value can help if an object with motion blur applied appears to lag behind the position of the object without motion blur applied.

Apply motion blur to a mask

Motion blur creates a blur based on the movement of a mask in the composition. You can apply motion blur to individual masks. Within each composition, the Enable Motion Blur composition switch must be selected for any layer or any mask within a layer to exhibit motion blur.

Additional resources about motion blur

When you shoot a fast-moving object, there is motion blurring when the object is rendered. Also, if you shoot moving objects with a high shutter speed, the objects appear to jump between frames leading to strobed motion.

The Pixel Motion Blur effect in After Effects CC tracks the movement of pixels between frames. The effect analyzes a clip to determine what parts are in motion, creates a set of motion vectors, and then uses that information to add motion blur within the frame.

If the object moves too fast, increase the value of Shutter Samples to create more in-between frames. Increase the value of Vector Detail to minimize the possibility of errors when pixel groups are analyzed between frames. 

Chris and Trish Meyer have provided a video tutorial for Pixel Motion Blur effect in the ProVideo Coalition website.

Todd Kopriva has blogged about this effect in the After Effects official blog.

For more information about other time effects in After Effects, see Time effects.

Mark Christiansen explains some of the concepts surrounding motion blur, shutter speed, and shutter angle on the ProVideo Coalition website.

Andrew Kramer provides a video tutorial on his Video Copilot website in which he demonstrates the advantages of using 32-bpc color with motion blur. (See Color depth and high dynamic range color.)

Smooth motion and velocity by removing extra keyframes

Smooth motion paths, value curves, and velocity curves to eliminate bumpiness or excess keyframes using the Smoother, which adds keyframes or removes unnecessary keyframes.

Although you can smooth a curve for any property, the Smoother is most useful when applied to curves automatically generated by Motion Sketch, where you may have excess keyframes. Applying the Smoother to keyframes that have been set manually may result in unexpected changes to the curve.  

When you apply the Smoother to properties that change spatially (such as Position), you can smooth only the spatial curve (the curve defined by the motion). When you apply the Smoother to properties that change only in time (such as Opacity), you can smooth only the value and velocity curves (the curve defined by the value or the velocity).

In addition to adding keyframes or eliminating unnecessary keyframes, the Smoother also applies Bezier interpolation at each keyframe when smoothing the temporal curve. (See Keyframe interpolation methods.)

Add randomness to a property with the Wiggler

You can add randomness to any property as it varies over time by using the Wiggler.

Depending on the property and the options you specify, the Wiggler adds a certain number of deviations to a property by adding keyframes and randomizing interpolations coming into or out of existing keyframes. You need at least two keyframes to use the Wiggler.

Using the Wiggler, you can more closely simulate natural movement within specified limits. For example, add randomness to an animated butterfly to produce fluttering. Simulate the flicker of an old projector by adding it to brightness or opacity.

Convert audio to keyframes

The Convert Audio To Keyframes keyframe assistant analyzes audio amplitude within the work area and creates keyframes for audio amplitude.

This keyframe assistant creates an Audio Amplitude layer representing all audio sources in the composition, with three Expression Controls effects with Slider properties that contain the keyframes: Left Channel, Right Channel, and Both Channels.

To use the keyframes created by this keyframe assistant, link the changes in audio amplitude to other layer properties. For example, use an expression to link the audio keyframes to the Scale property of a layer to make the layer grow and shrink as the amplitude increases and decreases.

Online resources for converting audio to keyframes

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.

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.

Lloyd Alvarez provides a script on his After Effects Scripts website that adds markers, splits a layer, or adds a text layer with incrementing numbers based on audio intensity.

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.