Use track IDs in sequences

Use track IDs in sequences

A track ID uniquely identifies an object across multiple frames in a sequence. Track IDs are essential for tracking applications where you need to follow the same object over time.

Understanding track IDs

When you create an object in a sequence:

• A unique track ID is automatically assigned

• The track ID remains constant across all frames where the object exists

• Track IDs increment sequentially, starting from the highest existing ID

Track IDs are visible:

• In the sidebar next to the object category

• In the timeline at the left of each track row

The timeline interface is described in detail in Track timeline.

Update a track ID

Change a track ID across all frames:

1. In the timeline, right-click on the track row

2. Select Update track ID

3. Enter the new track ID in the dialog

4. Click Update

Track IDs must be unique within the sequence. If you enter an existing ID, you'll be prompted to merge the tracks instead.

Use case: Fix incorrectly assigned track IDs or align with external tracking data.

Merge tracks

Combine two tracks that represent the same object:

1. Right-click on the source track row in the timeline

2. Select Merge with track

3. Choose the target track ID from the dropdown

4. Confirm the merge

All keyframes from the source track are transferred to the target track, and the source track is removed.

Important constraint: Merging tracks is only possible when both tracks have no overlapping keyframes.

Use case: Correct tracking errors where the same object was accidentally assigned multiple track IDs.

Split a track

Divide a track into two separate tracks at a specific frame:

1. Navigate to the frame where you want to split

2. Right-click on the track row in the timeline

3. Select Split track

The track is divided:

• Frames before the split point keep the original track ID

• Frames from the split point onward receive a new track ID

Limitation: Splitting a track is only possible if there are keyframes before the current frame.

The Split track action is only available in single-sensor sequences.

Use case: Separate objects that were incorrectly tracked as one, or handle scenarios where one object becomes two (e.g., a vehicle splitting into two paths).

Remove a track

Delete an entire track from the sequence:

1. Right-click on the track row in the timeline

2. Select Remove track

3. Confirm the deletion

This deletes all keyframes and annotations associated with the track. Use undo if you need to recover it.

When a track is removed, the highest track ID becomes available for new objects. Lower IDs require manual adjustment if you want to reuse them.

Same-dimensions constraint

For 3D cuboid sequences, you can enforce consistent object dimensions across all frames:

1. Go to Settings > Labeling

2. Enable the Same-dimensions track constraint checkbox

When enabled, all keyframes in a track will maintain the same object dimensions (width, height, depth), allowing only position and rotation changes between frames.

Note: The same-dimensions track constraint is only available for cuboid sequences.

Use case: Label objects with known fixed dimensions (e.g., standard shipping containers, vehicles with known specifications).

For more details on the timeline context menu and interface, see Track timeline.