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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 mp4 format videos only. Most smartphones record movies in this format. Movies from
iPhones have a different file extention (.mov instead of .mp4) but work just the same. Depending on your
web browser, your phone settings might need to be changed. If your Chrome version is earlier than
104 and you can't update (as will be true for older Chromebooks), or you otherwise made a video and it won't
play, then you need to record your videos using the H.264/AVC format. This can be done through the camera
settings on your phone. The setting you want will be called "most compatible" or dissed as
"less efficient". Use The Google to figure how to change this on your phone.
Do not edit the video on your phone. This scrambles the location of key information in the video file.
While I may, at some point, figure out how to unscramble things, the strategy for now is to download the
video from the phone without making any edits.
This should feel more or less like every other video playing app you've used. There's a play/pause button, a
button to reset the video to the start, and a pair of buttons to step one frame forward or one frame
backward. The progress bar can be used to jump to any point in the video, or dragged to move through it at
pretty much any speed you like. 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. 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.
This is an optional step. 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 this, 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. 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...BUT read the next paragraph.
The timing of videos that have been grabbed off YouTube can be pretty messed up. This can show up as
duplicate frames or missing frames. The Skip This Frame button is designed to address this. If you click
to take a data point and you do not see the video image change, then you are looking at a duplicate frame.
Click the Skip This Frame button. Sometimes the next frame will be a duplicate too. Just use the button
again. But be aware that this is probably only a partial fix. If there are duplicate frames, then the
there is a good chance that the whole time base for the video is off, and you are likely to get problematic
values for things like the acceleration due to gravity. If you have access to a video editor, and the
required expertise, you can maybe fix it. Otherwise, you will have better results making your own movies.
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.
In the Church of iPhone, a slow motion video will report that its playback frame rate is the frame rate
actually used when filming it. When you play the video, it plays back at the same high frame rate, and so
appears to be at normal speed. To get accurate motion timing, you do not need to adjust the time base. In
the Church of Android, the video reports its frame rate as 30 fps, so that playback appears in slow motion.
In that case, you do need to adjust the time base. Controls for that are at the bottom of the
app window, towards the right.
