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TLDR
Load a video, and then work your way down the left-side buttons from Calibrate down to Get Data Points. Use
the single step buttons to position the video to the frame you want to set as t = 0. The
zero positions for x and y are not critical. Set them wherever you like. When you are done
tracking the object, use the buttons at the lower right to copy the data into the clipboard for pasting into
a spreadsheet or nPlot. If all else fails, try reading the longer instructions below.
Sigmund Video Analysis Program
This browser-based app is designed to allow the video tracking of a moving object, like a tossed ball. The
basic idea is simple: load a movie, use an object in the video to set the scale, and then click on the
moving object in successive video frames to get position vs. time data. Sadly, it will not run properly on a
smartphone, only on a Chromebook or other laptop.
Videos & Video Format
This program works with the mp4 format videos produced by Android and Apple smartphones. (iPhone video files
have the extension .mov instead of .mp4, but work just the same.) This program will work best if you keep
it simple: take short videos with no slow motion.
Do not edit the video on your phone. This scrambles the location of key information in the video file.
If you want a short video, take a short video.
Slow motion videos are tricky! Slow motion is not generally needed for videos of dropped or gently
tossed balls. If you need slow motion to record your video of, for example, a fastball, please see the
Slow Motion section below.
Problem videos As phone technologies advance, new, more efficient video formats are developed. This program
uses your browser's built-in video player to show your video. Sometimes there is a lag between when a new format
shows up in phones and web browsers get updated to handle it. If you get a message that your video failed to load
properly, you will need to change your camera settings to an older format. In the worst case, you will need to
choose what is known as the H.264/AVC format. Use The Google to figure how to change this on your phone.
This should feel more or less like every other video playing app you've used. There's a play/pause button and a
button to reset the video to the start. There are a pair of buttons to step one frame forward or one frame
backward (you can also use the left and right arrow keys on the keyboard for this).
The progress bar can be used to jump to any point in the video, or can be dragged to move through it. If you drag
the bar too fast, you may have to reload your video. To the right of the progress bar is a display to show you
which frame you're looking at, and the total number of frames in the video.
By default, videos are muted when they first load. The control to unmute or re-mute the video is under the
progress bar.
A time stamp giving the time of the
current frame is shown in the lower right corner of the video area. The zero of time is either the first frame, or the
frame you set it to (see Setting the Origin below).
The Skip This Frame button is
explained in the Taking Data section below.
If you were planning ahead, there is something like a meter stick in your video. Press the Calibration button
to start. Click on the video where you want to start defining a line of known length, then click again where
you want that line to end. Enter the actual length of this line and the units for that length in the popup
window. The units in the data table headings will be updated to reflect your input. The calibration line will remain
on the screen. You can toggle the display of the length value with the Show Scale button. You can re-do the
calibration if you think you messed up, but you will lose any collected data.
There are three buttons. The t = 0 button sets the zero of time at whatever
frame is currently displayed. You set the positions for the zeroes of x and y with the cursor.
You can re-do any or all of these steps, but if you have collected any data, you will lose it. The Show Origin will toggle
the display of the x and y axes you just set up. It will also scroll the video to show the frame you set as
t = 0. This can be useful for quickly resetting the video to the point where you started taking data.
If you do not set an origin, the point (0,0) will be in the upper left corner of the video, and t = 0
occurs at the first frame.
Click the Get Data Points button to start. Each time you click on the image, you will get a red dot, and the
position of the dot will be loaded into the data table. When you click, the movie will automatically be moved
ahead by the Frame Advance number in the lower left. For a regular speed video of a dropped object a Frame
Advance of 2 works well.
If the movement of the object is small, the red dots can make it difficult to see things. You can hide the points
(with the Hide Points button) while taking data. Everything will work the same, you just won't get that red dot
when you click.
Click the Done button when you have finished, or Cancel to erase all your data and start over. (This does
not affect the calibration or zero point.)
Acquiring a new set of data (by clicking Get Position Data again) means erasing the old set. Be sure you have
copied that data to the clipboard (and pasted it into a spreadsheet!) before proceeding. If, for some reason,
you don't want to save the old data, just lie and say that you have.
While you are tracking an object, the video controls remain active, so you can use them to move forward or
backward before clicking the next point. The player always knows what frame it is showing, so the time
information will always be correct for videos you took yourself...BUT read the
Slow Motion section below if you are analyzing a movie clip you got from
YouTube or you took your video using the slow motion setting on your camera.
You can upload the horizontal and vertical postions (vs. time) separately. Pressing either the "x vs. t "
or "y vs. t " buttons will copy two columns of data to the clipboard so that
you can paste them directly into nPlot or some other graphing program. (But why would you want to use any
other program?) If you want column headers with the data (for pasting into an electronic lab notebook) hold
down the shift key while pressing the button. For your convenience, there is a Launch nPlot button right below the copy data
buttons.
Use this tool to measure distances in the video. If there is no calibration set, the distance will be reported
in screen pixels. The interface works just like the calibration: click at one end of the distance you want to
measure, then click again at the other. Hold down the shift-key while clicking the Measure button to clear all
the previous measurements.
Slow motion is tricky. Different phone brands handle the time information differently. Some brands change how the time information
is handled, depending on which version of iOS they are running. If you took your video in slow motion, and the frames per second
display (next to the Skip This Frame button) matches how you took the video, things should be fine. If the fps display doesn't
match what you did, then you will have to set the frame rate manually. Use the input in the bottom right corner (below the Frame
Advance control) to enter your actual frame rate, and click the checkbox.
Movie clips from YouTube Movie cameras run at 24 frames per second. YouTube videos run at 30 frames per second. A
YouTube clip taken from a movie will have duplicate frames. If you single-step through the clip, you will see that sometimes
what you are looking at does not change even though you have stepped to the next frame. This is a duplicate frame. To analyze
a movie clip, use a manual frame rate of 24 frames per second. Then, when you get a duplicate frame, click the Skip This Frame
button. (Sometimes you get two duplicate frames in a row. If the frame does not change when you click the button, click it again.)
