Chapter 24: Motion Tracking
Motion tracking pins a layer to something that moves in your footage — a screen to a laptop, a logo to a passing van, a label to a face. FX Express does not compute tracks; it imports them from After Effects or Mocha and applies them to a layer.
What you need
A track exported as one of:
| Source | Format |
|---|---|
| After Effects | ”Keyframe Data” copied from the timeline and saved as .txt |
| Mocha | Corner-pin export as .aec |
Three track shapes are understood:
| Kind | What it drives |
|---|---|
| 4-point corner pin | Full perspective placement — corner to corner |
| 2 points | Position, rotation, and scale |
| 1 point | Position only |
Sparse keyframes are densified to one value per frame at the source frame rate on import, so the layer follows the track smoothly regardless of how the export was keyed.
Importing a track
- Select the layer that should follow the track. Tracking is available on text, image, video, shape, and smart-object layers — not on groups or scene layers.
- Scroll to the Motion Tracking section at the very bottom of the Layer properties.
- Click Import tracking data… and choose the
.txtor.aecfile.
On success the section shows the file name, the track kind, the frame count, and the source duration and frame rate — e.g. corner-pin.txt · 4-point corner pin · 240 frames · 8.0 s @ 30 fps. Problems with the file are listed in red under the section rather than thrown away.
Tracking replaces the layer’s own transforms. While it is enabled, the tracked quad drives placement, rotation, and scale; the Transform section’s position/rotation/scale values stop having an effect.
Tuning
| Control | Range | Use |
|---|---|---|
| Enabled | on/off | Turn the track off to reposition the layer by hand, then back on |
| Offset X / Offset Y | ±50% of canvas | Nudge the layer off the tracked point |
| Scale | 0.5–2× | Grow or shrink about the tracked quad’s centre |
| Time offset | 0 – track duration | Trim seconds off the start of the track, in whole source frames |
| Motion blur | on/off | Render-only directional blur along the tracked motion |
| Strength | 0–3 | How much blur, once motion blur is on |
Motion blur is render-only. The editor canvas shows the layer sharp; the blur appears in the rendered movie. Preview a render before judging the setting.
Replace… swaps in a different track file while keeping the layer. Remove deletes the track and hands the layer back to its own transforms.
Workflow
- Track the shot in After Effects or Mocha and export the data.
- Bring the footage into FX Express as a video layer.
- Add the layer that should ride the track — a text label, a logo image, a screen replacement image.
- Import the track onto that layer.
- Set Time offset so the track lines up with where the footage starts in your scene.
- Nudge with Offset X/Y until it sits where you want it.
- Enable motion blur if the movement is fast, and check it in a render.
Troubleshooting
The Motion Tracking section isn’t there. The layer type doesn’t support it. Groups and imported scene layers are excluded; put the track on a real layer instead.
The import reported errors.
The section lists what the parser objected to. The commonest cause is exporting the wrong properties from After Effects — you want the corner-pin or position/scale/rotation keyframe data, with its Units Per Second, Source Width, and Source Height header intact.
The layer follows the motion but is out of sync. Use Time offset to trim the head of the track. It steps in whole source frames, so it can always land exactly on a frame boundary.
Moving the layer on the canvas does nothing. That’s the design: tracking overrides the layer’s own transforms. Use Offset X/Y, or untick Enabled.
The blur doesn’t show. Motion blur is applied by the renderer only. Run a preview render.
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