2D Video Tracking

Tracking is similar to image annotation, but each object can appear in multiple images. We can use bounding boxes or polygons to track the instances across the frames. The labels of the same instance in the exported label file will have the same label id.

An example of tracking results

2D Bounding Box Tracking

In the labeling interface of video tracking, move the slider around to move across frames.

Bounding box interpolation

Create a bounding box at the first frame it appears, and adjust the bounding boxes in the subsequent frames. For a given bounding box track, the frames in which the box is edited are considered a keyframe. The frames between keyframes are automatically interpolated using the interpolation method selected during project creation.

Ending object track

For an object that disappears after certain frame, press Backspace at the frame of its last occurrence. The bounding box labels after this frame will be deleted.

Track Linking

Sometimes an object reappears in the frame due to occlusion or re-entrance, and track linking enables individual tracks to be linked as a single instance. Select a label, click “Link Tracks” or press Ctrl-L (Cmd-L for Mac users), and click on any other tracks that you want to link with this label. The tracks you choose to link appears in dashed lines. Click “Finish” or hit Enter to finish this operation.

Track linking for 2D bounding box does not allow the tracks to be linked to have overlapping frames; make sure to end object tracks correctly for all tracks before the linking operation.

Track Breaking

If you accidentally link two tracks that not belong to the same object. You can click “Break track” at the frame you want to break this track. After this operation, the original track will break into two tracks. The first one will have labels of the original tracks from frame 0 to break_frame - 1, the second one will contain labels of the original track start at break_frame.

Single frame addition/deletion

Under the default setting, when you draw a label at a given frame, this label will be propagated to the end of this video. Sometimes this is unnecessary. So we provide an operation to only draw label at the chosen frame. This could be enabled by drawing the label while holding s.

When pressing s, the label would only be added at the given frame

Also, the default deleting operation would delete all labels after the chosen frame. Sometimes we only want to delete labels at some specific frames. So we provide an operation that only deletes the label at the chosen frame, while not affecting the labels of other frames. To use it, press backspace while holding s.

When pressing s, the label would only be deleted at the give frame

2D Instance Segmentation Tracking

Track labeling for instance segmentation is similar with that for bounding box.