Filming Basics FAQ

What do I need to do a video analysis?

You will need:

A video camera (smartphone/tablet works just fine)

A calibration object (any object of known length- e.g., a meter stick)

Stickers/reflective tape to mark the points that are to be tracked

Where do I film from?

You film from the plane perpendicular to the plane that the movement is happening in – for example if you want to capture knee flexion and extension in the anatomical position, you would film from a “side-on” view. If you are filming hip abduction/adduction, then it would be from a “front-on” view etc.

What do I do with the camera?

Distance: You want to position the camera far enough such that small, but close enough that you can capture the movement without having to move the camera. Typically, as a rule of thumb, try to keep the camera at least 10 feet away from the person.

Angle: You want the camera to be positioned squarely with the plane of the motion – i.e. not tilted up or down.

Fixing the camera: Once you are satisfied with the positioning of the camera, “fix” the camera in place using a tripod or other arrangement. It is imperative that you do NOT move the camera until filming is complete.

If for some reason, the camera has to be moved, you have to film the calibration object again in the new spot.

Are there any settings I need to set on my camera/phone?

Avoid the “super slow motion” setting in your camera – if you are really doing any activity that requires this setting, please talk to the instructor first.

If you are using an Apple iphone/ipad, please disable the “high efficiency” setting during recording and instead choose the “most compatible” setting. This will allow the video to be in a format that Tracker can read directlyTurn-off-High-Efficiency-Mode-for-Recording-in-iOS

What is calibration and how do I calibrate my video?

Calibration provides a reference of size and distance in the video. This allows to take measurements on the video and make them into “real-world” units (i.e. m, cm etc.). Once your camera is fixed, film the calibration object at the same distance where you will have the actual person performing their movement.

Where do I put markers?

You will put markers at all joints of interest. Remember that if you are computing an angle, you will have to also mark the proximal and distal joints. For example, to identify the elbow angle, you will also have to mark the shoulder and the wrist joints.

If you choose not to put markers (or cannot put markers), that is also OK, but you will have to track the joints manually (like you did for one of the fingers in Lab 1)

Markers can be anything (stickers, tape etc.) – just make sure they have enough contrast with clothing (e.g., white stickers on dark colored clothing, or black tape on light colored clothing).

If possible, ask your participant to avoid wearing loose clothing so that it is easy to identify anatomical locations. You can attach tape at the joints (or over the skin directly) to help you track these markers.

What do I ask participants to do?

Provide “clear instructions” to the participant so that you can repeat them consistently (do not assume your participants will know). For example, instead of asking them to “walk” – be clear in “walk as fast as possible”, or “walk at a comfortable pace”. Similarly, if you are looking at a tennis serve, your instructions could be “aim for this target on the court”, or “serve as fast as you can”.

How do I transfer the videos to my computer to analyze on Tracker?

Most of you will likely be using a smartphone/tablet for filming. Use the USB cable to transfer videos directly to computer (Do NOT email videos to yourself because videos will be compressed, resulting in a loss of quality)