Videos

The term video in the discussion below refers to (a) a digital video file recognized by QuickTime (typically .mov or .avi), (b) an animated GIF file (.gif), or (c) a sequence of one or more digital images (.jpg or .png files or images pasted from the clipboard), referred to as an image video.

1. Opening a video

To open a video into a new tab, use the Open button or File|Open menu item. To import a video into an existing tab, use the Video|Import, Video|Replace or File|Import menu item.

In the file chooser, set the file type to Video Files and select the desired file. Tracker will open JPG and PNG images and image sequences, animated GIFs, and QuickTime MOV and AVI files.

Note: If Tracker cannot open a movie file, you may need to reinstall QuickTime. (Note: QuickTime is not available for Linux. To use Tracker on Linux, please see Tracker on Linux.)

2. Opening numbered image sequences

Tracker will automatically open a sequence of up to 1000 JPG or PNG images that are numbered sequentially. To open a sequence, select only the first image in the sequence.

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).

3. 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.

4. Adding and removing images from an image video

Once an image video has been created, you can 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.

5. Saving pasted images

When closing or saving 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.

6. Video clips

A video clip is a subset of frames in a video defined by a start frame, step size (number of frames per step), and 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 have step numbers 0, 1, 2, 3 and 4 that map to video frame numbers 3, 5, 7, 9 and 11, respectively.

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 in the clip inspector. To display the clip inspector, click the inspector button at the right end of the player.

The clip inspector shows thumbnail images of the start and end frames along with the current video clip settings. In addition, there are fields for setting a start time (time assigned to step 0), the time interval dt between steps (important for high-speed or time-lapse videos) and the play rate as a percent of normal playback speed.

Note: since point mass tracks require that you mark their steps for every frame in the clip, it is most efficient to define the clip before marking. Clip properties may be changed at any time, but previously unmarked frames will then require marking.

7. Using the video player

The player includes (from left to right):

- time/step/frame readout
- play/pause button
- slider
- step forward button
- step back button
- loop button
- clip inspector button.

You can drag the entire player by the left end to convert it to a floating window if desired.

Click the play/pause button to play the video at the rate specified in the clip inspector; click again to pause the video. Drag the slider to scan a video or move quickly to a desired frame.

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.

Click the readout to choose frame (number, measured from the beginning of the video), time (seconds, measured from the start frame) or step (number, measured from the start frame). The readout displays frame number by default.

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

8. Magnifying (zooming) a video

Click the zoom button on the toolbar (shortcut: press the Z key) to turn on a zoom tool that can be used to magnify the video image up to 8x. With the zoom tool on, position the zoom cursor over a region of interest and either (a) click the mouse or (b) roll the mouse wheel to zoom. Double-click the mouse to set the zoom level To Fit so the video image fits exactly in the main video view.

By default, the tool zooms in (mouse cursor and button display the zoom-in icon). Hold down the Alt key to zoom out (mouse cursor and button display the zoom-out icon).

Zoom button with zoom off, zoom-in and zoom-out icons

Another zoom option is to right-click the video and choose the desired zoom level from the popup menu as shown below.

9. Video filters

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

10. 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 or unmarked steps that are newly included in the clip. If this happens, correct the problem by resetting the start frame, step size and step count for the new clip.

11. Saving a video clip as a file

Tracker can save the current video clip, including filters, as a new QuickTime movie, animated gif or image sequence. The new video file(s) will have the same dimensions as the current video.

Note: QuickTime movie file sizes can be large since they are not currently compressed! Animated gif files are always compressed, but have only 256 colors.

To save a video clip, select the desired Video/Save Clip As... menu choice and use the file chooser to save the file.

12. Recording a video of the main view

Tracker can record any or all frames in the main view (video with filters, zoom level and visible track overlays) as a QuickTime movie, animated gif or image sequence. The recording will have the dimensions of, and record the image within, the current viewport in the main video view.

Note: QuickTime movie file sizes can be large since they are not currently compressed! Animated gif files are always compressed, but have only 256 colors.

To record a video, select the File/Record menu item. This will bring up the Video Capture Tool which allows you to control the frame capture process and preview the video before saving it.

Note: the video dimensions are those of the main view. To produce a smaller video, shrink the main view window and set the zoom level "To Fit" before starting the recording process. Any extra white space around the video image will be included in the recorded image (i.e., what you see is what you get!).