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U.S. Department of Justice, Office of Justice Programs, National Institute of Justice - NIJ.gov
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Operating Characteristics and Functionality Descriptions of Body Worn Cameras
Video and audio to record and export in a standard, open, non-proprietary format, including both Codec and Container, such that it can be replayed in freely available software (e.g., VLC player) without processing or conversion. Standard open formats should be used for interoperability. Examples include MP4 and MKV. Data formats that can only be viewed within manufacturer-specific replay software are not recommended.
VGA, HD 720P, and 1080 HD are predominant standard resolutions. The higher the resolution, the more storage is needed. Estimates below were created assuming H.264 compression with medium to high motion at 30 frames per second (fps) derived using a heuristic formula widely used in industry. Actual storage utilized is dependent on scene complexity and the motion of the video captured. Consider what sort of analysis may be conducted on the video before selecting a resolution. For example, if forensic video analysis is anticipated, a resolution less than VGA is not recommended.
VGA (640 x 480)
550–1,100 MB per hour (0.55–1.1 GB)
HD 720P (1280 x 720)
1,650–3,325 MB per hour (1.65–3.325 GB)
1080 HD (1920 x 1088)
3,750–7,550 MB per hour (3.65–7.55 GB)
Video Encoding/ Compression
Use of the lowest possible amount of compression in order to maximize the amount of information available to law enforcement. Consider what sort of analysis may be conducted on the video before selecting video encoding or compression. Examples include MPEG-4, H.264, and H.265. H.264 is an improvement over MPEG-4 compression. H.265 is a new standard which further reduces storage needs while maintaining viewing quality.
30 frames per second (fps) is a standard video frame rate. Higher recording speeds capture more motion detail but require increased storage. Frame rates lower than 25 fps suffer from increased motion blur.
Horizontal Field of View
Adequate to capture a majority of activity at a reasonable distance. This would likely require at least a 90 degree field of view. Wide angle lenses capture more of a scene, but distort the view and lose detail towards the edges of the frame. Software tools may be required to properly analyze or view the video from extremely wide angle video.
Device should be able to focus on all objects from about 1 foot away to infinity. Continuous autofocus or fixed focus should be employed for usability. Manual settings should be avoided as they can distract the user. Motion jitter and blur can be significant when the camera is moving. Automatic image stabilization can reduce this effect.
The system is capable of clearly capturing conversational speech at a distance of 3 feet without wind or excessive background noise.
Separate Audio Resolution and Encoding/ Compression
If the device will be used in a mode to record audio only, compressed audio requires less storage than video (4–60 MB per hour per microphone depending on desired quality). If high speech quality is needed, a sampling rate of at least 22 kHz with at least 24-bit capture is suggested per microphone. Higher values might be necessary to capture increased fidelity at a distance. Standard open encoding with speech quality resolution suggested. Examples include MP3 and WMA.
Cameras could record continuously or be user-triggered or event-triggered. Cameras take time to start recording video after being powered on and after recording is initiated. This recording latency period should be minimal.
Night-time/Low Light Functionality
Quality of video footage recorded in low light or night conditions should be useable. Visible flash and infrared illumination can increase the quality of video taken at night but will affect battery life. Low-light filtering, infrared, near infrared, and other low-light compensation technologies or mechanical filters can increase the quality of video taken in low light and severe weather conditions but can affect scene and motion detail.
Synchronization and Metadata
The device is capable of recording audio simultaneously and time synchronized with video. Consider the additional information that should be collected with the recorded material. Automatically generated data about the wearer, location, date, and time can be collected and packaged in the video format. Device clock must be synchronized with an external universal clock, either GPS or another source, when the unit is plugged in for absolute time of day to ensure accuracy.
The device prohibits recordings from being edited or deleted and should not overwrite existing data before they have been transferred. Systems that can export a hash value of files being transferred may provide an enhanced capability to demonstrate tamper resistance. Standard encryption such as AES can be employed to protect data and improve the management of lost devices and memory cards.
Recommend standard USB2/USB3 compliant connection (mini/micro) for charging and/or data transfer. USB3 is preferred as speeds are considerably faster. The connections should be standard on both the device and on any docking station. Data connections that use a proprietary form factor are not recommended.
Device exports all recorded footage to data archiving or data management system in its original file format and without loss of quality or associated metadata. Device should record an audit log which should include information such as device serial number and device events; e.g., on/off, charging, start/stop recording, remaining storage capacity.
Storage can be integrated into the device or provided on removable industry standard memory cards. Removable media has utility in terms of versatility and expansion but comes with security risks. Consider whether enough storage should be available to record a full shift by the officer wearing the device, such as 8–12 hours of non-volatile onboard storage. Loss of power must not cause data to be lost or corrupted.
Consider whether the battery should provide enough power to record a full shift by the officer wearing the device, such as an 8–12 hour battery life. Devices that do not run on rechargeable batteries are not recommended.
Device should withstand considerable and repetitive pressure, vibration, and mechanical shock. It should operate within a temperature range from very cold to very hot and be resistant to common environmental hazards, such as dust, condensation, water splashes, and RF interference.
Weight and Form Factor
Device should not distract or hinder the officer wearing the device from performing other job functions, especially ones related to officer safety. Cameras are designed with widely varying mounting methods and options. Device should be selected for maximum usability and safety.