Audio and video are the digitalized source of evidence that can be found at the scene of a crime or with the victim or the accused in the form of audio-video from mobile device or any CCTV footage. Such types of digital evidences are of utmost importance in civil or criminal cases. Therefore, audio and video forensics is the leading branch of forensic science in the digitalized era.
In forensic science, audio-video forensics forms three basic principles such as acquisition, analysis, and evaluation of audio and video recordings which are admissible in the court of law. One of the main tasks of audio and video forensic experts is to establish the authenticity and credibility of digital evidence. The forensic examination of audio and video is done in order to enhance the recordings to improve speech intelligibility and audibility of the sounds.
One of the primary tasks of forensic digital investigators to assist the crime scene investigators in order to find the conclusive proof via a number of scientific tools and equipments. After following the standardized procedure of crime scene investigation, at the time of evidence collection, the investigators must thoroughly search the suspected area and recover the evidence carefully. Such digital evidences must be protected from physical harm, environment, and heat.
Once the evidence is collected in a safe and secure manner, the proper documentation of evidence must be done in the form of notes or photography/videography. The documentation must include in which condition the evidence was found from the crime scene along with the name of the evidence collector, date, and time of evidence collection. All examination protocols are carefully examined and constructed for enhancement techniques that must be employed to the recovered evidence.
A variety of enhancement techniques can be employed on audio and video analysis. The techniques which are employed for video enhancement are as follows:
a. Sharpening: This step makes the edges of the images more clear and distinct.
b. Video Stabilization: This step reduces the amount of movement in the video, and also produces the fine playback.
c. Masking: This step covers the face or areas of the video that may protect the victim, witness or any law enforcement official.
d. Interlacing: In an analog system, the interlaced scanning is used to record the images or at the same time, this process is used to de-interlace which may be used to retrieve the information.
e. Demultiplexing: There is a device in CCTV named multiplexer, which is used to combine multiple series of video signals into a single signal.
a. Frequency Equalization: There is a need for highly precise equalizers that are used to cut specific bands of frequencies. The frequency band which often contains more speech content is amplified or isolated. Large noise or interruptions can be analyzed by spectrum analyzer and the corresponding frequencies are reduced in order to reduce noise level.
b. Compression: Faint or low sound can be increased by compressing or leveling the signal so that the loud range can be minimized.
Such evidences are critically analyzed and listened carefully and proper documentation must be done. After standard forensic protocol, the forensic report is prepared by a forensic cyber expert and presented in the court of law.
The forensic audio-video report must include the following details:
1. Results which were obtained from the analysis of audio-video files
2. Waveform charts of audio recordings and comparison waveform with formants
3. Identification of the format and type of recording
4. Type of processing which was used to analyze
5. Date and Time of analysis of audio files.
6. Description of the evidence in the type of circumstances and conditions in which it was collected
7. Description of the enhanced audio-video and type of software that was used.
8. Qualifications of the Audio Video Analyst.
9. Authorized signatory with name and stamp
10. Hash Values of the Audio Video Files.