Motion Tracking
Evidor can follow a moving object through a video clip, then either stabilize the shot or make another clip follow the same motion. The tools live in the Motion tracking and Attach to tracker sections of the inspector.
How it works
Evidor uses template matching. You draw a small box around the thing you want to track. The contents of that box become a template. Evidor then searches a small area around the template's previous position, in each frame of the clip, to find the location that best matches the template. The result is a list of positions, one per frame, that describes the object's motion.
Template matching works best on:
- High-contrast features: bright logos on dark backgrounds, corner points on objects, eyes, textured patches.
- Objects that stay roughly the same size and rotation throughout the shot.
- Short shots, ideally a few seconds. Longer clips accumulate error.
It struggles with:
- Objects that change size or rotate significantly.
- Uniform areas, such as a blank wall or a smooth gradient.
- Objects that pass behind other objects and disappear.
Tracking a point
- Select a video clip on the timeline.
- Move the playhead to the frame where the object you want to track is clearly visible.
- Open the Motion tracking section in the inspector. If the track is locked or hidden, unlock or show it first.
- Click Define region. The preview enters tracking mode with a yellow box in the center.
- Drag the box over the object. Use the eight small handles around the box to resize and move it. Keep the box tight; a smaller box tends to track better.
- Click Set region to confirm.
- Click Analyze motion. A progress bar appears as Evidor steps through the clip. Depending on the length and resolution, this can take a few seconds.
- Track the source clip as above. Confirm that it has tracking data by checking the Motion tracking section.
- Select the clip you want to follow. This is the "follower".
- Open the Attach to tracker section of the inspector.
- Pick the tracked clip from the Tracker source dropdown. Only clips that have tracking data appear there.
- Click Attach to tracker.
When analysis finishes, the section shows how many positions were found and over what duration. The clip gets a small yellow dot on the timeline to indicate that it has tracking data.
Stabilizing a clip
Once tracking data exists, click Stabilize clip. Evidor takes the first tracked position as the reference and computes a translation for each subsequent frame that would keep the tracked point fixed. Those translations become position keyframes on the clip.
The result is that the tracked point stays centered in the frame, which reduces camera shake. Stabilization does not correct rotation or scale changes, only X and Y translation.
Attaching a clip to a tracker
You can make a clip follow the tracked motion of another clip. This is how you attach a logo to a moving object, or a title to a person's face.
Evidor converts the tracker's positions into position keyframes on the follower clip, offset by whatever position the follower already had. If the follower was centered, its position now moves with the tracked point. If it was offset to the side, it stays offset to the side but follows every movement.
The attachment is not live. Once attached, the follower has its own keyframes. Changing the source tracker afterwards does not affect it.
Clearing tracking data
The Clear button in the Motion tracking section removes the region and the tracked positions from the selected clip. If stabilization has already been applied, its keyframes are also removed. The clip returns to its pre-tracking state.
Using the data elsewhere
Positions are stored as normalized coordinates from 0 to 1, so they survive any resolution change. The keyframes produced by the stabilize and attach operations are ordinary position keyframes and can be edited, extended, or removed from the Animation section of the inspector.
The maximum number of tracked positions per clip is 10,000. Most real-world shots use a few hundred to a few thousand.