Tracker can analyze three different video types:

  1. digital video files (.mov, .avi, .mp4, .flv, .wmv, .ogg, etc.) which require a video engine (see below).
  2. animated GIF files (.gif).
  3. images and image sequences consisting of one or more digital images (.jpg, .png, zip or pasted from the clipboard; see below).

Tracker uses the Xuggle video engine to open most digital video files including .mov, .avi and .mp4 on all platforms. Tracker online uses the HTML5 engine to open .mp4 and other web video formats.

1. Opening or importing a video from a local drive

The easiest way to open a video in a new tab is to simply drag and drop it onto the Tracker toolbar. You can also use the Open button or File|Open File menu item. To import a video into an existing tab, drag and drop it into the main video view or use the Video|Import, Video|Replace or File|Import|Video menu item. Select the desired video in the file chooser to open it.

Open button File|Open menu item Video menu

2. Opening a video from the web

The Digital Library Browser provides access to individual videos or collections of videos and tracker files on the web. Open the library browser by clicking the Open Library Browser button or choosing the File|Open Library Browser menu item. For help using the library browser, see Digital Library Browser.

OSP Digital Library Browser

3. Image Video: opening image files

An image video is a video type consisting of one or more images that Tracker treats as video frames. Images can be JPG or PNG files, or they can be pasted directly from the clipboard.

Image files that have the same filename with sequential numbering (e.g., image0.jpg, image1.jpg, image2.jpg, image3.jpg, image4.jpg) can be automatically opened into a single image video (in this case, with 5 frames). To open a sequence, select only the first image in the sequence (in this case, image0.jpg).

Image sequences may be compressed into a zip file to reduce size and simplify handling. Tracker opens zipped image videos automatically, and can export video clips directly to zipped image videos.

Image sequence numbering must have a fixed format. For example, selecting the first image in a sequence numbered image00.jpg to image14.jpg will open all 15 images, but if the sequence is numbered image0.jpg to image14.jpg then only the first 10 images will be opened (i.e., up to image9.jpg).

4. Image Video: pasting images from the clipboard

Images that have been copied to the clipboard may be pasted directly into Tracker for analysis. Choose the Video|Paste Image or Video|Paste Image|Replace Video menu item to create a new image video.

5. Image Video: adding and removing images

Once an image video has been created, you can edit it to add or remove frames. You must first enable editing by checking the Video|Enable Editing checkbox. This reads all image files into memory so that the video is independent of the file system.

With editing enabled, paste or import additional images using the Video|Paste Image or Video|Import Images menu choices Before This Frame or After This Frame.

To remove images from an image video use the Video|Remove This Frame item.

When importing images you can select multiple images in the file chooser by control-clicking or shift-clicking.

Importing images

6. Saving pasted images

When you stop editing, close or save an image video that contains pasted images, a warning dialog prompts you to save the images as files if desired. You must save the images if you wish to reopen them at a later time.

Saving images

7. Video clips

A video clip is a subset of frames in a video called steps. The steps in a video clip are defined by:

  1. start frame
  2. step size (number of frames per step)
  3. end frame

The start frame is the frame number of the first step, the step size is the frame increment between successive steps, and the end frame is the frame number of the last step. For example, a clip with start frame 3, step size 2 and end frame 11 would consist of step numbers 0, 1, 2, 3 and 4 that map to video frame numbers 3, 5, 7, 9 and 11, respectively. (Note: the end frame must be an integer number of steps downstream from the start frame.)

A clip is defined for every video and even for null videos. For single-frame and null videos the clip settings apply to tracks but every step maps to the same video image.

Video clip properties are set with the video player and/or the clip inspector.


8. Clip settings

To display the clip settings, click the Clip Settings button on the toolbar Clip settings button.

The clip settings dialog shows the current video clip settings and also provides fields for setting a start time (time assigned to step 0), the true frame rate (important for high-speed or time-lapse videos) and the time interval dt between frames (inverse of the frame rate).

Clip inspector dialog

9. Using the video player

The player includes (from left to right):

Click the readout and select the display type: frame number (measured from the beginning of the video), time in seconds (measured from the start time) or step number (measured from the start frame). The readout displays frame number by default.

Player readout options

Click the readout and set the time at the current frame by choosing the Set time... item from the dropdown menu. Note: this action changes the times at all frames in the video.

Choose the Go to... item from the readout or Video menu, or type control-G, to display the Go To dialog. Enter a desired frame, time or step and click OK or hit the Enter key to jump directly there.

Use the rate spinner to set the play rate (% of normal) or enter a desired rate directly in the field.

Click the reset button to reset the video to step 0, or use the keyboard shortcut HOME. To move immediately to the end of the video, use the keyboard shortcut END.

Click the play/pause button to play the video; click again to pause.

Drag the slider to scrub the video or move quickly to a desired frame. You can also use the mouse wheel to scrub by choosing the Scrub option in the preferences dialog or holding down the control key. Holding down both control and alt keys scrubs by 10 frames at a time.

Drag the black in- and out-point markers to set the start and end frames.

Setting in point

Right-click the slider to access many of these actions in a popup menu.

Setting in point

Click the step button to step forward one step, or use the keyboard shortcut PageDown. Click the back button to step back one step, or use the keyboard shortcut PageUp. Hold down the shift key with these actions to step by 5 steps instead of 1.

Click the step size control to set the step size in frames per step.

Click the loop button to toggle looping (continuous play).

10. Magnifying (zooming) a video

There are four ways to change the magnification of the video for more accurate marking:

  1. Click the zoom button on the toolbar and choose the desired zoom level from the dropdown menu as shown in below. Tip: Double-click the zoom button to set the zoom level To Fit so the video image fits exactly in the main video view.
  2. Position the cursor over a region of interest and roll the mouse wheel forward to zoom in, back to zoom out.
  3. Right-click on a region of interest and choose Zoom In, Zoom Out or Zoom To Fit from the popup menu.
  4. Drag a zoom box using the right button and choose Zoom In to zoom to the box as shown below.
  5. Press the Z key (mouse cursor displays a zoom icon) and click or drag the mouse to zoom in. Hold down the Alt key at the same time to zoom out.

Zoom button dropdown (left) and right-click popup (right) menus

Right-drag and zoom to the box

11. Video filters

Video filters allow you to modify the video image. See video filters for complete filter descriptions.

12. Hiding and closing a video

Uncheck the Video|Visible menu item to hide the video image and display the tracks on a white background. Choose Video|Close to remove the video permanently.

Note: when removing or replacing a video, a new video clip is created. This may result in some tracks having existing steps that are no longer included in the clip or unmarked steps that are newly included. If this happens, correct the problem by resetting the start frame, step size and end frame for the new clip.

13. Exporting a video clip

Tracker can export the current video clip as a digital video file, animated GIF or image sequence, thus serving as a simple video editor and transcoder. But exported videos can also include track overlays, video filters, and additional views like world views and plots, making them useful for documenting the video modeling or analysis results. Interlaced 30 fps videos can also be exported as 60 fps deinterlaced videos, which doubles the temporal resolution while halving the vertical resolution.

Note: the exported video contains only frames in the current video clip (determined by start frame, step size and end frame), not the entire video.

Export video clip menu item

To export a video clip, select the File|Export|Video Clip... menu. This will bring up the Export Video Clip dialog.

Exporting a video clip

Select the view, content, size and format of the exported video from the dropdown lists. The content choices depend on the selected view as follows:

  1. Main view: Video and graphics, Video only, Graphics only or Deinterlaced Video
  2. World view: Video and graphics or Graphics only
  3. Other views: Graphics only