Motion tracking overview and resources



With motion tracking, you can track the movement of an object and then apply the tracking data for that movement to another object—such as another layer or an effect control point—to create compositions in which images and effects follow the motion. You can also stabilize motion, in which case the tracking data is used to animate the tracked layer to compensate for movement of an object in that layer. You can link properties to tracking data using expressions, which opens up a wide variety of uses.

After Effects tracks motion by matching image data from a selected area in a frame to image data in each succeeding frame. You can apply the same tracking data to different layers or effects. You can also track multiple objects in the same layer.

For information about Imagineer Systems mocha for After Effects, see Tracking and stabilizing motion.

Uses for motion tracking and stabilization

Motion tracking has many uses. Here are some examples:

  • Combining elements filmed separately, such as adding video to the side of a moving city bus or a star to the end of a sweeping wand.

  • Animating a still image to match the motion of action footage, such as making a cartoon bumblebee sit on a swaying flower.

  • Animating effects to follow a moving element, such as making a moving ball glow.

  • Linking the position of a tracked object to other properties, such as making stereo audio pan from left to right as a car races across the screen.

  • Stabilizing footage to hold a moving object stationary in the frame to examine how a moving object changes over time, which can be useful in scientific imaging work.

  • Stabilizing footage to remove the jostling (camera shake) of a handheld camera.

    Depending on the encoder you use, it is possible to decrease the size of your final output file by stabilizing motion footage. Random motion, such as from the jostling of a handheld camera, can make it difficult for many compression algorithms to compress your video.

Motion tracking user interface and terminology overview

You set up, initiate, and apply motion tracking with the Tracker panel.

As with all properties, you can modify, animate, manage, and link tracking properties in the Timeline panel.

You specify areas to track by setting track points in the Layer panel. Each track point contains a feature region, a search region, and an attach point. A set of track points is a tracker.

Layer panel with track point

A.
Search region

B.
Feature region

C.
Attach point

Feature region
The feature region defines the element in the layer to be tracked. The feature region should surround a distinct visual element, preferably one object in the real world. After Effects must be able to clearly identify the tracked feature throughout the duration of the track, despite changes in light, background, and angle.

Search region
The search region defines the area that After Effects will search to locate the tracked feature. The tracked feature needs to be distinct only within the search region, not within the entire frame. Confining the search to a small search region saves search time and makes the search process easier, but runs the risk of the tracked feature leaving the search region entirely between frames.

Attach point
The attach point designates the place of attachment for the target —the layer or effect control point to synchronize with the moving feature in the tracked layer.

Note: When you begin tracking, After Effects sets the quality of the motion source layer to Best and the resolution to Full in the Composition and Layer panels, which makes the tracked feature easier to find and enables subpixel processing and positioning.

After Effects uses one track point to track position, two track points to track scale and rotation, and four points to perform tracking using corner pinning.

Online resources for motion tracking and stabilization

Curtis Sponsler provides detailed instructions and explanations for tracking and stabilizing motion in a PDF excerpt from his book The Focal Easy Guide to After Effects.

Chris and Trish Meyer provide a video tutorial on the ProVideo Coalition website that demonstrates and explains the basics of motion tracking.

Angie Taylor provides a tutorial on the Digital Arts website that shows how to use tracking data and the Clone Stamp tool to apply copies of an object in a scene while matching a camera move.

Michele Yamazaki provides a tutorial on the Toolfarm website that shows how to use motion tracking to obscure a logo in motion footage.

Sean Kennedy provides a set of detailed tutorials on the SimplyCG website that demonstrate advanced motion tracking techniques:

Sean Kennedy provides a free script, TrackerViz, that makes tracking motion and applying tracking data to masks easier. You can get Tracker Viz and a series of detailed instructions on the SimplyCG website.

The Visual Effects for Directors series provides tips about preparing and shooting for motion tracking and compositing, both using point trackers and planar trackers. Free sample videos include “How to place tracking markers” and “How to shoot for planar tracking”.

Eran Stern provides a video tutorial on the Artbeats website that demonstrates the use of 3D tracking software that solves for camera movement so that additional elements can be composited into the scene and appear to honor the same camera movement. This video tutorial uses Pixel Farm PFHoe, but the techniques can be applied to almost any matchmoving software.

This post on the AE Enhancers forum describes and links to an animation preset from Donat van Bellinghen for scaling a set of Corner Pin effect points.

This post on the AE Enhancers forum describes and links to a script from Paul Tuersley that takes a stabilized layer, precomposes it, and then adds expressions that counter the stabilization.

This post on the AE Enhancers forum describes and links to a script from Paul Tuersley that can make a difficult tracking job easier by averaging multiple sets of tracking data.

Jeff Almasol provides a script on his redefinery website that creates a null layer with an expression that sets the Position property to be the average of the values of motion tracking track points for the selected layer.