Digital Video Recorders (DVR) and most video recording devices used in the security industry utilize compression to record the video on storage devices. Cameras have the ability to capture much larger volumes of data than is required to depict the scene back to the human eye. The recording systems are not able to record all the data that the cameras are capable of viewing. Compression is used to store the data onto storage mediums. There are many different types of compression / decompression programs or codecs. Some common types of codecs are H.264, MPEG, MPEG4, wavelet. Knowing how these compression’s work and how videos files are compiled and played back is essential in being able to accurately analyze video files. With thousands of combinations of cameras, settings, video compression types and storage limitations; the untrained eye will make assumptions about what is displayed on the screen when a surveillance video is played back. Often this assumption can lead to misunderstanding of what the video is actually depicting as it plays back. Dropped frames during recording and wrong playback speeds are a couple of the more common misinterpretations that occur when untrained personnel review video.
At AVA Ltd. we understand video, and how codecs compress and how it is decompressed during playback. We are then able to identify the best frames to be used for comparison to known items. The proper frame use during a comparison is essential to the accurate forensic comparative analysis.
AVA Ltd. has done video comparisons for various law enforcement agencies on criminal investigations including homicides, sexual assaults and robberies. Forensic analysis reports are provided complete with court charts in Adobe Acrobat format for review by clients. AVA Ltd. is here to analyse your video and obtain proper evidence from your surveillance video files and compare the video images to known items.
Below is a sample of what a comparisons report would show:
