The rise in the number of CCTV cameras and ‘dashcam’ has created huge potential for collision investigators. Historically, investigators have had to rely on sometimes subjective interpretations of physical evidence identified at the scene, or witness evidence. Video purports to present an objective truth: after all, “the camera never lies”. This term often worries video analysts, because whilst the camera cannot lie, its footage can mislead, if not managed appropriately.
To understand the events which led to a collision, video footage is being used increasingly to draw a whole range of conclusions relating to vehicle speed, pedestrian walking speeds, reaction times, and so on. These types of analyses invariably involve a frame-by-frame analysis of the footage which captured either the collision, or the lead-up to it. It has proved invaluable to investigators and the Courts.
The ability of an investigator to see exactly what happened can lead to more certainty in drawing conclusions about how the collision occurred, and the causative and contributory factors at play. The ability for a Judge, Coroner, or jury to have footage played to them also assists the Court in understanding what occurred. After all, that is the role of an expert witness: to assist the Court. If analysis of video improves an expert’s ability to help the Court, then its use is valuable.
Whilst the moving images forming part of a piece of footage are extremely useful, so too is the audio, which may have been captured along with it. Whilst not all CCTV cameras or dashcam can capture audio, an increasing number do. Often analysts rely on narrative descriptions of the audio stream contained within a piece of footage, but would those descriptions stand scrutiny? Are they simply one individual’s subjective opinion regarding what could/may be heard on a piece of footage, or is there a way to analyse the footage forensically, to provide a greater level of certainty, when presenting conclusions? Audio analysis provides that opportunity.
Forensic analysis of audio gained sudden fame and became headline news in the 1970s when 60 hours of audio formed part of the evidence that brought down the Nixon presidency following the Watergate scandal. The meticulous work of investigators discovered an 18-minute gap in the recordings captured by President Nixon. In November 1973, six technical experts were assigned to verify the integrity and originality of a set of these recordings. The set of techniques used by this team formed the basis for a new type of forensic practice, and the associated report became the manual. The scandal ultimately led to the resignation of President Nixon.
Clearly, not all cases will require audio analysis; in the same way that not all cases require video analysis, but there will be occasions where the audio is as equally important (or more so) as the video footage. One such example could involve using the audio to determine speed; a vehicle (or pedestrian) may pass a CCTV camera and go out of view prior to a collision occurring. Whilst the collision itself may not be captured on video, the sound of it may be. Whilst it may seem relatively straightforward to determine the elapsed time between the object leaving the video frame and the sound of the collision occurring, it is often more complex. Audio streams are not always synchronised with the associated video streams; if this is not accounted for, it may well inadvertently mislead the Court. It may also be the case that the audio stream has background “noise” or other artifacts which prevents sounds from being identified clearly. An audio analyst may well be able to isolate and/or reduce background noise or other artifacts. For this (and many more reasons) it is important to ensure that audio analysis is approached with the same level of care and skill as any other aspect of forensic science.
Those undertaking enquires into collisions would benefit from considering whether a piece of video footage contains audio, which may prove useful to the investigation. It is worth seeking advice on these matters, as opening a video in a default player may not always reveal the accompanying audio stream. TRL’s experts have experience in audio analysis and can assist in understanding whether it is possible to obtain audio from a piece of video footage whether it be from fixed CCTV cameras or ‘dashcam’.
Author: Craig Arnold – Consultant