Surveillance Tape Analysis

Recorded video can serve as a dynamic and effective tool for archiving, analyzing, and exhibiting data. Digital video now allows the user the same level of resolution, or greater, as typical still photography. Additionally, the video can record the motion of a vehicle, or an object such as a railroad crossing gate arm, not possible through a still photograph. The video also has the capability to record time-sensitive information that cannot be captured using a conventional camera.

Video can also be used as a means of extracting information, such as object measurements using the mathematical process of videogrammetry. Regardless of who recorded the video or when it was recorded, an engineer with the proper tools can often extract dimensional data such as the length of tire marks, location of gouges, or speed of vehicles from a video.

Once recorded, video can be a powerful means of exhibiting data. Whether the video consists of animations recorded to DVD, a sequence of still image captures, or a re-enactment of an event, video can demonstrate objects in motion in an accurate and realistic way.


Picture this… a police cruiser is sitting roadside, in a parking lot, monitoring traffic. We’ve all seen it. Some of us may even watch our rear-view mirror after passing by, hoping that he doesn’t pull out after us. Undoubtedly, at some point, he will spot a vehicle that appears to be traveling too fast, at which point he’ll use the tools available to him to approximate the vehicle’s speed. Having “confirmed” his suspicion, he pulls out and makes a traffic stop.
“Excuse me, sir; do you know how fast you were going?”

After the vehicle operator denies he was going too fast, the officer informs him he was going over 50 mph in a 35 mph speed zone. The defendant, being summoned to court for his infraction, still may not accept that he was traveling too fast. That’s where a review of the surveillance video may prove beneficial. Provided with the police dash cam video, a request is made to quantify the defendant’s vehicle speed, if possible, to see if there is a viable defense.

Knowing the year, make and model of the vehicle, the specifications for the vehicle are researched. Then, the dash cam video is broken down, frame by frame. The time-stamp on each frame allows for a determination of time passage from one frame to the next. Given the specifics of the defendant’s vehicle, namely the wheelbase in this particular instance, the vehicle speed was able to be quantified at approximately 52 mph, essentially confirming the excessive speed finding of the police.

Here’s How the Evaluation Was Done

  • The vehicle was a 2010 Dodge Grand Caravan, with a wheelbase of 121 inches.
  • The vehicle traveled the length of its wheelbase in 4 frames of the police dash cam video.
  • The video was recorded at 30 frames per second, or 0.0333 seconds per frame.
  • Speed is calculated as distance over time.
  • A distance of 121 inches (10.08 feet) divided by 0.1333 seconds (4 frames at 0.0333 seconds each) equates to a speed of 75.6 feet per second, or approximately 52 mph.

The defendant now knows where he stands.

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