Audio in Video Evidence

When performing audio and video authentication and analysis, a trained forensic expert will utilize several methods in an attempt to detect an edit in a video recording used as evidence. Often times, a critical ear is just as important to a video forensic expert as the scientific community accepted software tools and an established chain of custody.

Sound Analysis


A picture is worth a thousand words. However, an audio file can be worth even more in a video forensic laboratory. A trained video forensic expert knows what to look and listen for during a forensic video authentication and analysis investigation.

Many CCTV systems now have the capability to record audio. And this audio portion of the surveillance video recording can be crucial to the legitimacy of the digital video evidence. Audio is a great tool to investigate an anomaly or edit when investigating a video recording. To do so there’s a process and protocol we follow at Primeau Forensics.


Sound pressure waves are the building blocks of audio, which are representative of the change in air pressure in a recording. One characteristic of sound pressure waves is that they are always smooth and continuous.

For example, you’re recording in an open, quiet room. While you’re recording, a rebellious teenager comes in the room and blows off his air-horn. Even though that loud sound completely changed the overall sound in the room, the wave that represents the pressure change will always be smooth and continuous.

The only time that a wave is not smooth and continuous is when an edit occurs. A recording edit disturbs the waveform. This makes it temporarily rigid and inconsistent. All sound pressure waves should be the opposite of that. So, when I am critically listening and hear a sound outside of that smooth, uninterrupted audio file, I know I have an anomaly that may be an edit.

How is that disturbance represented? Well, it will usually manifest itself in the form of a pop. In the context of video, it usually will only last a frame, but the sound will be there. If you hear anything that deviates from the already established waveform, editing occurred.


Adobe and Izatope RX have software that allow a forensic experts to more accurately detect these edits. For example, a spectrogram detects the noise floor in a recording. The spectrum recorded for a noise floor should be consistent in visual characteristics as long as nothing changes with the ambiance in a recording. When you see a deviation in that consistency, just as if you hear one in the dialogue, you have altered audio, and subsequently altered video.

There are many ways to detect edits visually when reviewing digital video evidence. Establishing a chain of custody, as well as performing forensic video authentication and analysis, will reveal integrity in your video recording or anamolies if the CCTV video recording has been comprised.

Increase in Body Worn Cameras and Video Evidence for Trial

In the last few years, Primeau Forensics has seen an increase in cases that involve surveillance video, including body camera video recordings. This digital video evidence is very important in order of investigators and the trier of fact to understand events as they occurred.


An increase in activity began in 2013 when body worn cameras helped locate and identify the Boston Marathon Bombers. FBI investigators culled through hundreds of hours of CCTV video surveillance recordings in order to identify the terrorists that responsible for these acts of violence.

Video evidence is expanding to include body worn cameras implemented into many police agencies across the United States. At this point in time, agencies around the country are testing different makes of body cameras and learning how to properly integrate them into their procedures. Many have been transparent with their testing and have begun to approve funding for additional cameras.

The Grand Rapids, Michigan Police Department recently tested two different kinds of body worn cameras among its officers. Following their positive feedback, the city approved funding for two hundred additional cameras. The Seattle, Washington Police Department has also been very open about their body camera testing. They even released testing footage online for public view. The public has been pushing for police worn body cameras since the Michael Brown shooting in Ferguson, Missouri last August.


Body worn cameras protect everyone; police officers and citizens alike. Many police agencies fully support camera use because they reduce the questioning of events during an altercation. If a disagreement comes against an officer, internal affairs can check the body camera video and see the events as they occurred. Police agencies believe this will be very helpful with training officers and improving the relationship between the public and police.

The biggest issue arising from the increase in body worn cameras is the amount of data being created. Video evidence requires a very large amount of secure storage. Thankfully, many companies providing these cameras also include proprietary software. This ensures the evidence remains unaltered between the camera and the system. Only authorized personnel have access to the video to maintain the authenticity and safety of the video evidence.


As video forensic experts, we see many benefits to this increase in body worn cameras. We have worked on numerous cases in which evidence from these cameras greatly helped the investigation and proceeding trial. Police dash cameras have often been used as evidence, but they fail to the capture the entire altercation because of their stationary view. Police body worn cameras add a second perspective used along with the dash cam which can be invaluable to an investigation. Having two angles provides a better picture of what happened.

All video recordings submitted as evidence in a civil or criminal litigation must have an established chain of custody that supports the events and provides integrity for the digital video evidence. We also encourage you to review our series on How to Properly Record a Police Officer.

Video Evidence | South Carolina Officer Shooting Unarmed Black Man

A South Carolina police officer was arrested yesterday for the murder of an unarmed black man. This is all because of video evidence that surfaced of the North Charleston officer, Michael Slager, firing eight times at the unarmed man as the man fled in an open field.

North Charleston Michael Slager Shooting Slager


According to police reports, the victim in question, 50-year-old Walter L. Scott, continued to flee after being hit by the officer’s stun gun. The reports also state that Mr. Scott took Officer Slager’s stun gun, which lead to a reasonable pursuit.

However, the video seems to show a different story. First, the stun gun is dropped. Second, the officer guns down Mr. Scott and drops something next to the unarmed man. It is not clear what was dropped; however, some fear that this was planted on the man after his shooting, as police report that the officer’s taser was taken.


In either case, the innocent bystander who recorded the Good Samaritan video aided in this investigation. Not only did he take the responsibility to record the events, but he also utilized landscape mode on his cell phone to record the altercation. As a result, we’re provided with additional digital video evidence for this investigation.

As you see in the first few seconds of the video, portrait orientation would not have accurately captured the events as they occurred. Mr. Scott would have run off screen and we never would have seen this happen. However, because he shot the video in landscape mode, we see the shooting clearly.

Situations like this help reinforce the importance of the devices in our pockets. Smartphone video can make or break a case like this and we need to understand why it’s so crucial to utilize the tools we have when an unlawful event occurs. If it weren’t for the Good Samaritan, this story may have gone unseen and unnoticed.

You can watch the video below via the NY Times here