AUDIO AND VIDEO FORENSICS


Audio and video forensics refers to the acquisition, analysis, and evaluation of audio and video recordings that may be used as evidence in court.


Audio and Video Forensics

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Audio and video forensics refers to the acquisition, analysis, and evaluation of audio and video recordings that may be used as evidence in court. Unlike other forensic evidence, recordings can provide real-time account of a crime. But for most crimes, high-quality recordings are not often available, which raises problems such as whether the evidence is authentic and credible. Thus, the main concern of audio and video forensic examination is to establish the authenticity of the evidence, perform enhancement to the recordings to improve speech intelligibility and audibility of the sounds, and interpret and document evidence (e.g., identifying talkers, reconstructing crime or accident scenes, and establishing timeline.)

Principles of Audio and Video Forensic Examination

Examiners assist in crime scene investigations using a number of tools and techniques. According to the National Forensic Science Technology Center, the principles of forensic audio and video analysis are the following:


    1. Repair and Recovery of Evidence

    Evidences such as audio and video recordings must first be recovered or repaired from damaged media or device. This is common for analog and digital magnetic tape.

    Modern devices today can be easily damaged by heat, misuse,environmental conditions on crime scenes, and the offender.


    2. Evidence Enhancement

    Enhancement of recordings is needed to improve the quality of the recording and to make it easier when used as evidence for clarity and credibility. This can be done through the use of filters and speed of playback


    3. Analysis, Interpretation, and Identification

    Examiners inspect recordings for any alterations and present them as authentic evidence. Ambient sounds can tell whether the recording changed place suddenly, volume and tone of voices can tell the distance and spatial relationships in a crime scene, and lighting conditions can estimate the time and environmental conditions at the time of the recording.


How is audio and video analysis done?

Examiners perform series of observations and tests to evaluate the integrity of the evidence:

1. Collection of evidence – several different recordings of an event may be available depending on the surroundings and witnesses (e.g., surveillance systems and phone cameras).

2. Compression – documentation of the condition and properties of the evidence recording

3. Critical listening or watching – carefully observing the recording and taking note of apparent alterations or irregularities.

4. Report preparation and writing – creating a report on whether the evidence is authentic based on the analysis of observation.

The report may provide the following details:

    a. Results obtained from the analysis of recording
    b. Identification of the format or type of recording
    c. Type of processing used
    d. Date and time stamps that were visible
    e. Description of the subjects in the recording
    f. Description of the enhanced video or audio
    g. Limitations in the analysis

Techniques used in Audio and Video Analysis:

A number of techniques are used for enhancing audio and video recordings.

Video Enhancement:

    1. Sharpening
    2. Video stabilization
    3. Masking
    4. Interlacing
    5. Demultiplexing

Audio Enhancement:

    1. Frequency equalization
    2. Compression


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It is a capital mistake to theorize before you have all the evidence. It Biases the Judgement

Sherlock Holmes