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Multi-frame bounding box

Alex Cota Updated by Alex Cota

You can use the Multi-frame bounding box tool to apply a bounding box to a series of frames and manipulate the size and the position of the bounding box across the frame sequence.

The following is not supported:

  • Text or dropdown classifications in export
  • Toggle on/off bounding box on a selection of frames
  • Undo/redo actions
  • Change an existing bounding box class
  • Copy/paste a bounding boxes on multiple frames at a time
  • Create multi-frame bounding boxes via the API
  • Exports for mixed media (e.g. videos & images in the same project)

Import video data

First, create your project in Labelbox and ensure your videos are in .mp4 format. To learn how to import your video files directly, see Direct upload. To learn how to import your video URLs via JSON, see Import via JSON. To learn how to attach metadata to your imported videos, see Asset metadata via JSON.

To learn how to import programmatically, see Bulk add data rows.

Free tier users will be able to load videos with up to 20,000 frames and 30fps.

Set up Multi-frame bounding box

  1. Create a project.
  2. Select "Editor" as your label editor.
  3. Click "Add object" and name the object class.
  4. Select "Bounding box" as your labeling tool.
  5. [OPTIONAL] Create nested classifications. Note: only Radio and Checklist are supported.
  6. Click "Confirm".
  7. Click "Complete setup".

How it works

There are three main components to multi-frame bounding boxes:

  • The selected frames to persist the bounding box
  • The size of the bounding box
  • The bounding box position on the frame(s)

A keyframe is a frame on the timeline where a change occurs. Interpolated (tweened) frames the ones between two keyframes. Labelbox uses interpolation to incrementally adjust the size and position of bounding boxes between keyframes.

Apply bounding box to one or more frames
  • Apply a bounding box at a single keyframe. By default, when you apply a bounding box when a single frame is selected, that bounding box will persist with the same size and position across all subsequent frames until the end of the video.

  • Apply a bounding box to a set of frames. When you select a set of frames on the timeline and apply a bounding box to the selection, the bounding box will persist with the same size and position across each frame in the selection.
  • Toggle on/off a bounding box. When an item in the video goes out of frame then reappears 1 or more frames later, use the toggle icon to turn on/off the bounding box for that item.
Toggle on/off is only possible when a single frame is selected. You cannot toggle the bounding box on or off when multiple frames are selected.

  • Copy/paste a bounding box. When you copy and paste a bounding box from one frame to another, its position and size are preserved. A new bounding box instance is created out of the copied object and, by default, the bounding box will persist until the last frame in the video.
Copy/paste on multiple frames at a time is not supported.

Edit location and size
  • Update bounding box position and/or size. When you change the position/size of the bounding box in the middle of the sequence, Labelbox uses interpolation (also known as tweening) to incrementally adjust the bounding box to its new position/size. The updated bounding box position/size will persist until the end of the sequence.

  • Insert bounding box between interpolated frames. When you adjust the size and/or position of a bounding box between two already interpolated keyframes, Labelbox will interpolate the frames to adjust for the newly inserted keyframe.

Delete bounding box

Right click on the bounding box to delete the entire instance of the bounding box in every frame it appears. You can also do this with the backspace key.

Create instances

When a video is loaded in the Editor, you can create multiple instances of the Bounding box object.

  1. Select the bounding box class from the "Tools" panel.
  2. Select the same bounding box class again.
  3. Draw the next instance of the bounding box.

Export labels

For instructions on how to access your multi-frame point labels and a sample Multi-frame bounding box label export, see our docs on Label export formats - video.

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