Accuracy of Time Stamps in Digital and Network Video Recorders

Video analysis plays a major role in many forensic fields. Many articles, publications, and presentations have covered the importance and difficulty in properly establishing frame timing. In many cases, the analyst is given video files that do not contain native metadata. In other cases, the files contain video recordings of the surveillance playback monitor which eliminates all original metadata from the video recording. These “video of video” recordings prevent an analyst from determining frame timing using metadata from the original file. However, within many of these video files, timestamp information is visually imprinted onto each frame. Analyses that rely on timing of events captured in video may benefit from these imprinted timestamps, but for forensic purposes, it is important to establish the accuracy and reliability of these timestamps. The purpose of this research is to examine the accuracy of these timestamps and to establish if they can be used to determine the timing between frames. Four recording devices and six cameras were utilized with varying configurations. All videos recorded the Axon VFR Lightboard as the control measurement. Videos were recorded with each device and each camera configuration at 30, 15, and 4 frames per second. Once recorded, each video was processed using Axon Investigate’s “VFR Lightboard Calculator” to establish the actual timing between each frame. Subsequently, ten timestamp seconds within each video were compared to the actual elapsed time reported by the Lightboard. In total, 54 videos were recorded across all configurations. This study demonstrates the timestamp is not always accurate from second to second. However, a pattern was observed, and a methodology was developed. The average error between the theoretical time and the actual time reported by the Lightboard was 2.99 milliseconds (approximately 0.3%). The maximum error between theoretical and actual time for any timestamp second was 22 milliseconds (approximately 2.2%).