Track or stabilize motion



Tracking motion and stabilizing motion are essentially the same process, only with a different target and result. Use Track Motion to track motion and apply the results to a different layer or effect control point. Use Stabilize Motion to track motion and apply the results to the tracked layer to compensate for that motion (for example, to remove camera shake).

To stabilize a layer, After Effects tracks the motion of a feature in the layer that should be stationary in the frame, and then uses the tracking data to set keyframes to perform the opposite motion. You can stabilize to remove any combination of changes in position, rotation, and scale, while leaving desired motion unaffected. For example, if the camera is panning, deselect Position but select Scale and Rotation as the properties to stabilize.

When you select Rotation or Scale in the Tracker panel, you set two track points in the Layer panel. A line connects the attach points; an arrow points from the first attach point (the base) to the second. If possible, place the feature regions on opposite sides of the same object, or at least on objects that are the same distance from the camera. The farther apart the regions, the more accurate the calculations and the better the result.

After Effects calculates rotation by measuring the change of angle of the line between the attach points. When you apply the tracking data to the target, After Effects creates keyframes for the Rotation property.

After Effects calculates scale by comparing the distance between attach points on each frame with the distance between the attach points on the start frame. When you apply the tracking data to the target, After Effects creates keyframes for the Scale property.

When you track motion using either parallel or perspective corner pinning, After Effects applies keyframes for the Corner Pin effect to the layer to scale and skew the target layer as necessary to fit the four-sided area defined by the feature regions. The feature regions should lie in a single plane in the real world—for example, on the side of a bus, on the same wall, or on the floor. The attach points should also all lie in a single plane, but not necessarily the same plane as the feature regions.

Note: For parallel corner pinning only: To change which point is inactive, Alt-click (Windows) or Option-click (Mac OS) the feature region of the point to make inactive. (One point must remain inactive to keep the lines parallel.)
  1. Select the layer to track in the Timeline panel.
  2. Do one of the following:

    • Click Track Motion in the Tracker panel (or choose Animation > Track Motion), click Edit Target, and choose the target to apply the tracking data to.

    • Click Stabilize Motion in the Tracker panel (or choose Animation > Stabilize Motion). The target layer is the tracked (source) layer.

  3. Select Position, Rotation, and/or Scale to specify what kinds of keyframes to generate for the target.
  4. Move the current-time indicator to the frame from which to begin tracking.
  5. Using the Selection tool, adjust the feature region, search region, and attach point for each track point.
  6. In the Tracker panel, click either the Analyze Forward or Analyze Backward button to begin tracking.

    If the tracking ceases to be accurate, click the Stop button , correct the problem as described in Correct a motion track, and resume analysis.

  7. When you are satisfied with the position of the feature region and attach point throughout the track, click the Apply button to apply the motion to the specified target.

    After Effects creates keyframes for the target layer.

    When tracking position and applying this position data to a target, you can choose to apply only the x (horizontal) or y (vertical) component of motion. For example, you can apply the tracking data to the x axis to make a speech bubble (the motion target) remain at the top of the frame even when the actor (the motion source) moves downward.

    • X And Y (default) allows motion along both axes.

    • X Only restricts the motion target to horizontal movement.

    • Y Only restricts the motion target to vertical movement.

    To bypass the Motion Tracker Apply Options dialog box and use the previous setting, hold Alt (Windows) or Option (Mac OS) as you click Apply.
Note: You can change the order of steps 1-3 by first selecting the property to which to apply the tracking data (Scale, Position, or Rotation) and then choosing Animation > Track This Property. After Effects prompts you to choose the layer to use as a motion source.

When you stabilize a layer, the compensating motion may itself cause the layer to move too far in one direction, exposing the background in the composition or moving action out of the action-safe zone. You can correct this with a small change in scale for the layer. Find the frame where the problem is most severe, and then increase or decrease the scale of the layer until the problem is resolved. This technique adjusts the scale for the duration of the layer; you can also animate scale to correct this problem by zooming in and out at different times.

Motion tracking controls

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

Motion Source
The layer that contains the motion to track.
Note: Layers are available in the Motion Source menu if they have source footage items that can contain motion or if they are composition layers. You can precompose a layer to make it available in the Motion Source menu.

Current Track
The active tracker. You can modify settings for a tracker at any time by selecting the tracker from this menu.

Track Type
The tracking mode to use. The motion tracking itself is the same for each of these modes; they differ in the number of track points and how the tracking data is applied to the target:

  • Stabilize tracks position, rotation, and/or scale to compensate for movement in the tracked (source) layer. When tracking position, this mode creates one track point and generates Anchor Point keyframes for the source layer. When tracking rotation, this mode creates two track points and produces Rotation keyframes for the source layer. When tracking scale, this mode creates two track points and produces Scale keyframes for the source layer.

  • Transform tracks position, rotation, and/or scale to apply to another layer. When tracking position, this mode creates one track point on the tracked layer and sets Position keyframes for the target. When tracking rotation, this mode creates two track points on the tracked layer and sets Rotation keyframes for the target. When tracking scale, this mode creates two track points and produces Scale keyframes for the target.

  • Parallel Corner Pin tracks skew and rotation, but not perspective; parallel lines remain parallel, and relative distances are preserved. This mode uses three track points in the Layer panel—and calculates the position of the fourth—and sets keyframes for four corner points in a Corner Pin effect property group, which is added to the target. The four attach points mark the placement of the four corner points.

  • Perspective Corner Pin tracks skew, rotation, and perspective changes in the tracked layer. This mode uses four track points in the Layer panel and sets keyframes for four corner points in a Corner Pin effect property group, which is added to the target. The four attach points mark the placement of the four corner points. This option is useful for attaching an image to an opening door or the side of a bus that’s turning a corner.

  • Raw tracks position only. Use Raw to generate tracking data that you won’t apply using the Apply button. For example, you can copy and paste the keyframes for the Attach Point property to the Position property for a paint stroke; or, you can link effect properties for the Stereo Mixer effect to the x coordinate of the Attach Point property using expressions. Tracking data is stored on the tracked layer. The Edit Target button and the Apply button are not available with this tracking option. You can add track points to a tracker by choosing New Track Point from the Tracker panel menu.

Motion Target
The layer or effect control point that the tracking data is applied to. After Effects adds properties and keyframes to the target to move or stabilize it. Change the target by clicking Edit Target. No target is associated with a tracker if Raw is selected for Track Type.

Analyze buttons
Begins the frame-to-frame analysis of the track point in the source footage:

  • Analyze 1 Frame Backward : Analyze the current frame by moving back to the previous frame.

  • Analyze Backward : Analyze from the current-time indicator backward to the beginning of the trimmed layer duration.

  • Analyze Forward : Analyze from the current-time indicator to the end of the trimmed layer duration.

  • Analyze 1 Frame Forward : Analyze the current frame by advancing to the next frame.

Note: While analysis is in progress, the Analyze Backward and Analyze Forward buttons change to a Stop button, with which you can stop analysis when the track drifts or otherwise fails.

Reset
Restores the feature region, search region, and attach point to their default positions and deletes the tracking data from the currently selected track. Tracker control settings and keyframes already applied to the target layer remain unchanged.

Apply
Sends the tracking data (in the form of keyframes) to the target layer or effect control point.

Motion tracking options

These settings apply to a tracker, a group of track points that is generated in one tracking session. You can modify these settings by clicking Options in the Tracker panel.

Track Name
The name for a tracker. You can also rename a tracker by selecting it in the Timeline panel and pressing Enter on the main keyboard (Windows) or Return (Mac OS).

Tracker Plug-in
The plug-in used to perform motion tracking for this tracker. By default, this option displays Built-in, the only tracking plug-in included with After Effects.

Channel
The components of the image data to use for comparison when searching for a match for the feature region. Select RGB if the tracked feature is a distinct color. Select Luminance if the tracked feature has a different brightness than the surrounding image (such as a burning candle carried through a room). Select Saturation if the tracked feature has a high concentration of color, surrounded by variations of the same color (such as a bright red scarf against a brick wall).

Process Before Match
Temporarily blurs or sharpens an image to improve tracking. Blur reduces noise in the footage. Usually a value of 2 to 3 pixels is enough to produce better tracks in grainy or noisy footage. Enhance exaggerates or refines the edges of an image and makes them easier to track.
Note: After Effects blurs or enhances the layer only for tracking. This blurring does not affect the motion source layer.

Track Fields
Temporarily doubles the frame rate of the composition and interpolates each field to a full frame to track motion in both fields of interlaced video.

Subpixel Positioning
When selected, keyframes are generated to a precision of a fraction of a pixel. When deselected, the tracker rounds off values to the nearest pixel for generated keyframes.

Adapt Feature On Every Frame
Causes After Effects to adapt the tracked feature for each frame. The image data that is searched for within the search region is the image data that was within the feature region in the previous frame, rather than the image data that was in the feature region at the beginning of analysis.

If Confidence Is Below
Specifies the action to perform when the Confidence property value is below the percentage value that you specify.
Note: To determine an acceptable confidence threshold, track the motion and then examine the Confidence values for the track point in the Timeline panel for problematic frames. Specify a confidence value that is slightly larger than the largest confidence value for the problematic frames.

  • Select Continue Tracking to ignore the Confidence value. This behavior is the default behavior.

  • Select Stop Tracking to stop the motion tracking.

  • Select Extrapolate Motion to estimate the position of the feature region. Attach-point keyframes aren’t created for low-confidence frames, and attach-point keyframes for the low-confidence frames from previous tracks are deleted.

  • Select Adapt Feature to use the original tracked feature until the confidence level falls below the specified threshold. At that point, After Effects adapts the tracked feature to be the contents of the feature region in the frame preceding the one that has low confidence and continues tracking. This option isn’t available if Adapt Feature On Every Frame is selected in the Motion Tracker Options dialog box; enabling feature adaptiveness causes After Effects to adapt the feature region with every frame regardless of the confidence level.

Options
Opens the Tracker Plug-in Options dialog box, which includes options for the AE Original Built-in Tracker. This command is only available if you choose to use the older After Effects tracker plug-in.

Motion tracking properties in the Timeline panel

Each time you click Track Motion or Stabilize Motion in the Tracker panel (or choose Animation > Track Motion or Animation > Stabilize Motion), a new tracker is created for the layer in the Timeline panel. Each tracker contains track points, which are property groups that store the tracking data after tracking has been performed. Trackers are grouped in the Motion Trackers property group for each layer in the Timeline panel.

To show a tracker in the Timeline panel, select the tracker from the Current Track menu in the Tracker panel and press SS.

You can rename trackers and track points and modify and animate their property values in the Timeline panel just as you do for other layer properties and property groups. You must click Apply in the Tracker panel to apply the property changes to the target.

Feature Center
Position of the center of the feature region.

Feature Size
Width and height of the feature region.

Search Offset
Position of the center of the search region relative to the center of the feature region.

Search Size
Width and height of the search region.

Confidence
Property through which After Effects reports the amount of certainty regarding the match made for each frame. In general, Confidence is not a property that you modify.

Attach Point
Position assigned to the target layer or effect control point.

Attach Point Offset
Position of the attach point relative to the center of the feature region.