The purpose of this document is to provide recommendations and
guidelines for the use of closed-circuit television (CCTV) security
systems in commercial institutions, such as banks and convenience
stores. For the purpose of this document, stationary unattended
cameras and on-site recording devices will be discussed. The basic
principles and recommendations can, in most cases, be applied to
any system using CCTV cameras and video recorders. This document
addresses analog and digital video systems. The intent of these
recommendations and guidelines is to optimize image quality to facilitate
the identification of unknown people and objects depicted therein.
This document does not specifically address employee theft or other
internal security issues, although some of the recommendations can
be applied to those problems. Likewise, this document does not address
live monitored surveillance systems. References that address such
systems are included in Appendix A, References.
Furthermore, these guidelines are not intended to replace or take
precedence over other regulatory requirements in the specific jurisdiction
of the facility to which these guidelines will be applied.
The use of CCTV systems and the recording of security images is
an accepted practice in commercial institutions, such as banks,
convenience stores, and other facilities. In addition to deterring
crime, this practice can often facilitate the apprehension and conviction
of people involved in criminal activity. It is the position of the
Scientific Working Group on Imaging Technology that in order to
optimize the use of these systems, the following criteria should
This document addresses electronic CCTV security recording systems
only. It does not address the use of film-based or digital-still cameras.
This document is not intended to suggest removing film surveillance
systems or digital-still cameras from the affected facilities. Due
to the fact that images recorded using film and digital-still cameras
are usually of higher quality than video images, the continued use
of such systems, where existing, is strongly encouraged.
- Recordings that depict criminal activity must be preserved
in a manner that permits law enforcement officials to recover
the original images with a documented chain of custody. (Chain
of custody is the chronological documentation of the movement,
location, and possession of evidence.)
- The number, placement, and type of cameras should be sufficient
to provide adequate coverage and detail in the monitored area.
- There should be adequate, balanced lighting in the monitored
- Institutions should establish and follow a program of regular
- Institutions should have documented procedures to ensure that
employees know what to do in the event of a criminal incident.
A CCTV security system may include a single camera or multiple
cameras. Coverage can include checkout areas, walk-up or drive-up
automated teller machines, public-service areas, entrance or exit
doors, work areas, interior corridors or common building hallways,
and exterior or interior parking areas.
A camera system may include cameras, a monitor to view the camera
images, a recording device to capture selected images, or software
or a switching system to control the method of selecting and storing
images. Depending on the location and situation, video-camera systems
may use an analog videocassette recorder (VCR) , a digital video
recorder (DVR), or a PC-based digital recording capture station
to record images from the cameras. Finally, a means of retrieving
and storing images must be incorporated into the system.
This document addresses CCTV systems in the following seven areas:
- System Design (Section 5)
- Recording Systems (Section 6)
- Cameras (Section 7)
- Media (Section 8)
- System Maintenance (Section 9)
- Retention of Recordings (Section 10)
- Evidence Handling (Section 11)
4. Functional Requirements
The purpose of these requirements is to increase the likelihood
that images recovered from CCTV systems are sufficient to enable
law enforcement officials to identify the people and objects of
interest depicted therein.
In order to identify a person, specific individual features on a
person, such as the detailed shape of the eyes, ears, nose, mouth,
and chin, must be distinguished. Identification is facilitated if
the ability to distinguish smaller features such as moles, scars,
tattoos, and freckle patterns, as well as the ability to derive
measurements of these features, is possible. (CCTV systems that
were designed for automated facial recognition may not meet the
minimum standards specified in this document.) Likewise, identifying
a vehicle requires that the license plate numbers or other identifying
characteristics be distinguished.
In Figure 1, the images on the left are more likely to allow for
personal identification than the images on the right. The lower
part of the figure shows the head of the subject from each image
after it has been enhanced.
Figure 1(a). A Closed-Circuit
Television Image Likely to be Suitable for Personal Identification.
Figure 1(b). A Closed-Circuit
Television Image Not Likely to be Suitable for Personal Identification.
Figure 1(c). Cropped, Enlarged,
and Enhanced Image Processed from Figure 1(a).
Figure 1(d). Cropped, Enlarged,
and Enhanced Image Processed from Figure 1(b).
5. System Design
The ability of a CCTV system to record images that will be of greatest
assistance to law enforcement depends on multiple factors including
the choice and placement of cameras and lenses, recorders, storage
space, and compression schemes. These factors are not independent
of one another but must be coordinated with one another. As an example,
adding cameras to an existing system may require adjustments to the
amount of storage or the rate at which images from each camera are
A careful survey of the facility in which the system will be installed
must be completed and analyzed as an integral part of the total system-design
process. A site plan documenting the location and field-of-view of
each camera in the facility should be included as a part of this survey.
Finally, upon installation, the system must be tested to confirm that
images produced by the system as output (i.e., those that would be
provided to law enforcement in the event of a criminal investigation)
are of sufficient quality to maximize the likelihood of identifying
people or objects depicted therein.
5.1. System Components
CCTV systems should include the following components, at a minimum:
a camera or cameras, moveable and/or fixed; a monitor; and a recording
device, including the means by which the recording may be extracted
from the device. Consideration should also be given to any need
for recording audio with the video from one or more cameras and
any legal problems unique to audio recording. Guidelines for recording
devices are addressed in the following subsections and in Section
6, whereas cameras are addressed in the following subsections
and in Section 7.
A monitor should be included with every CCTV system so that system
operation may be checked on a daily basis (see Section 9). Monitors
capable of operating in an under-scan mode are strongly recommended
because this capability permits the viewer to observe the entire
field-of-view being recorded.
5.2. Number and Placement of Cameras
The number of cameras needed for an institution will vary depending
on a variety of factors, including the specific security needs
of the institution and the monitored area(s). Care should also
be exercised to ensure that cameras are not located in places
where they may be subject to tampering or accidental adjustments.
Camera disabling and tampering can be minimized by using components
that feature concealed wiring and protection of the camera and
lens assembly from weather and/or physical damage.
The cameras' fields-of-view should not be obstructed, nor should
cameras be pointed directly at bright light sources, such as picture
windows and spot lights. If bright areas cannot be avoided in
a scene, cameras with backlight illumination or compensation adjustments
are preferred to optimize the resulting image.
As a minimum, there must be at least one camera for every exit.
These exit cameras should be aimed toward the interior of the
facility, and each one should be located where it can obtain an
unobstructed frontal view of the head and shoulders of everyone
exiting the facility. The lenses on exit cameras should be configured
to have a depth-of-field that extends from three feet to at least
ten feet from the camera in order to provide images of exiting
people that are in focus. Exit cameras that have a depth-of-field
extending from three feet to beyond ten feet will have the added
benefit of providing overviews of the interior and head-to-foot
views of people as they enter and exit the facility.
Cameras should be placed where they can record images with unobstructed
views at each point of customer transactions, such as teller windows
(walk-up and drive-through), cash registers, automated teller
machines, or customer-service stations. There must be at least
one camera at each point-of-customer transaction. Cameras should
be adjusted to ensure that they are in focus at the location where
a customer can be expected to stand. If a window or other security
barrier is present, care must be taken to position the camera
in a manner that minimizes reflection, glare, and other obstructions
that can interfere with a clear view of the persons or objects
Figure 1(a) illustrates a head and shoulders image that is preferable
for the exit and transaction cameras. The camera lenses needed
to achieve the fields-of-view are discussed in Section 7.
Cameras that provide overviews of the interior and exterior portions
of a facility can be useful in an investigation but cannot be
relied on to provide images suitable for identification purposes.
Therefore, in these guidelines they are considered to be of reduced
importance. However, if the combination of the exit and customer-transaction
cameras do not provide complete coverage of the interior of the
facility, then it is recommended that additional cameras be included
for this purpose.
If deemed necessary, exterior cameras intended to record images
of vehicles should be placed to provide direct views of the vehicle
so that the license plate is clearly visible and legible. Additional
exterior cameras covering wider fields-of-view can provide additional
Finally in some instances, commercial institutions may find it
useful to include monitored cameras as a part of their overall
security strategy. The views from such cameras are not intended
to be recorded but provide employees with a means to view areas
in a facility that would otherwise be out of employees' sight.
Moveable dome and pan/tilt cameras can be used to provide additional
room coverage through automatic alarm presetting and parking.
Motion detection or door contact alarms can automatically initiate
a camera preset providing a high-resolution view of the alarmed
scene. This provides unmanned, additional target coverage. After
a predetermined time, the camera can return to a preset parked
position or to a scanning pattern to cover site locations not
viewed by the fixed devices.
If the system contains a matrix switch with a joystick controller,
a guard or observer can manually track a suspect giving a tightly
zoomed, high-resolution image of the suspect. Variable speed control
and automatic focus are recommended to facilitate smooth target
tracking. When in the parked position, the unit can serve as an
additional fixed camera.
Specific information regarding camera types and lenses is provided
in Section 7.
Poor lighting is the most common factor that degrades the quality
of video images. Adequate, balanced lighting should be provided
in areas viewed by the cameras. Particular care must be taken
to ensure that the dynamic range present in a scene does not exceed
the capability of the camera to record it.
Strong backlighting or high-contrast lighting may cause the face
of a subject to be obscured in shadow, making identification of
a suspect from the image difficult or impossible. Likewise, spotlights
can create both shadows and highlights on faces, making it difficult
to determine if observed tonal variations represent actual features,
such as facial hair, or are merely a product of the lighting.
The use of noninfrared, high-dynamic range cameras and those capable
of operating in low light conditions should be considered to help
improve the image quality.
As an example, ceiling-mounted fluorescent lighting that is well
distributed throughout interior spaces would be preferred to the
use of track-mounted spotlights.
Finally, different light sources have different color temperatures
that will affect the apparent color of objects in a scene. Tungsten
lamps impart a reddish tint to objects in a scene, whereas fluorescent
bulbs can impart a greenish tint. Likewise, sodium lamps can make
objects appear more yellow than they actually are. Most color
video cameras can be adjusted to compensate for this, and many
perform this function automatically.
A color video camera is considered balanced for a particular reference
white when a neutral white card is placed in the camera's
field-of-view under normal illumination conditions and the red,
green, and blue channels provide equal output levels. Therefore,
interior color cameras should be balanced for white on installation
and rebalanced if the type of lighting used is changed. However,
because many commercial institutions will operate under conditions
in which lighting is variable, white balance may not be possible
at all times.
Infrared lighting can be used to provide improved low light performance
for monochrome cameras. Infrared lighting is not supported by
standard color cameras as they filter out the infrared spectrum.
If an infrared sensitive video camera is used, law enforcement
officers should be made aware of this because an infrared sensitive
video camera often reproduces clothing that appears to be dramatically
differently when compared to images of the same clothing that
were recorded with a video camera that is not sensitive to infrared.
A more complete set of technical guidelines for lighting is provided
in Appendix B.
5.4. Electrical Power
CCTV systems must be provided with adequate power. Backup power
sources and surge protection should be included in the system
design to ensure that recordings are preserved in the event of
a power loss. Systems that require electrical power to preserve
their recordings should have backup power sources sufficient to
last for at least 30 minutes, until either the system power is
restored or the system is shut down in a manner that preserves
the recording. Video processors such as DVRs should also automatically
restart in a preprogrammed operation mode on power-up from extended
When a VCT or DVR with automatic restart is used, there must be
an ON-OFF switch on the front of the recorder. This is to ensure
that no data is lost following an incident that led to the recorder
being purposely turned off to preserve the recording of the event.
CCTV systems should be placed on isolated circuits that are properly
grounded to reduce interference and signal degradation. If the
system is on a long power run, outdoors, or in an area prone to
electrical storms, special protection devices to control power
surges and nearby lighting strikes are strongly recommended.
The bandwidth provided for transmitting the video signal must
be compatible with, and sufficient to meet, the resolution requirements
listed below for the system's recording device. Although bandwidth
minimum standards do not guarantee acceptable video image quality,
they do play an important part. To improve the likelihood of acceptable
image acquisition, video cameras should have a signal bandwidth
of at least 7MHz.
Signal-to-noise ratio: One major problem with picture clarity
is noise. Electronic noise is present to some extent in all video
signals. Noise manifests itself as snow or graininess over the
whole picture on the monitor and subsequently on recordings. There
are several sources of noise: poor circuit design, heat, overamplification,
external influences, automatic gain control, and transmission
systems. Some video signal noise cannot be overcome in a reasonable
manner. However, to improve the likelihood of acceptable image
acquisition, video cameras should have a signal-to-noise ratio
of at least 48dB. Further, the line loss between each camera and
the multiplexer or recorder that the camera is connected to shall
not cause the signal to fall below 45dB.
5.6. Recorder Security
Steps must be taken to ensure the physical security and integrity
of the system's recording device. Placement of the recording device
in a restricted access location, such as a locked cabinet or room,
is strongly recommended. Note that proper environmental controls
must be implemented according to the manufacturer's specifications.
For example, VCRs require adequate airflow to prevent overheating.
Policies should be in place to ensure that law enforcement can
gain immediate access to the recorded images when necessary.
5.7. Recordings of Associated Text Information
Both analog and digital CCTV systems include the capability to
associate text information, such as time, date, and camera identification,
with the images recorded by the system. In some cases, transaction
or personal information may also be recorded in association with
image data. This is often accomplished by superimposing the text
directly on the images.
Time, date, and camera information is useful in investigations
and should be preserved. However, text that obstructs the view
of subjects' faces or vehicles' license plates may hinder
investigations and should be placed to minimize its effect on
Test recordings should be performed to ensure that this requirement
is being met and that the information being recorded is accurate.
The Scientific Working Group on Imaging Technology strongly recommends
that digital CCTV systems be configured so that associated text
information is unalterable and preserved as data records or files
that are linked to the respective images. In such cases where
time and date, transaction, or personal information is recorded
in digital systems along with the image stream, it must be possible
for law enforcement to recover the images separate from this information.
For analog CCTV systems in which it is not possible to separate
personal or transaction data from the images, systems must be
configured to record this information for one second or less for
each instance (e.g., transaction) in which such data is required.
If the text information is visible on the recorded video, then
the text characters must be as small as possible while still being
legible, and it must be possible to position the text anywhere
on the screen to minimize the effect.
Each individual image and transaction data packet should have
a time/date stamp associated with it. Whenever possible the time/date
stamp should be generated as close to the image source as possible.
For example, when a camera is directly wired to the digital recording
device at the same site, then time synchronizing the recorder
is sufficient. However, when the camera is located remotely (in
another city) and connected to the recorder by a wide-area network
(WAN), then the image may be delayed in transit. In those cases,
it is highly desirable to associate the time stamp with the image
at the source sensor (the camera) instead of at the recorder.
A time-tag image file is then transferred over the WAN to the
recorder. The trend toward using Internet-protocol (IP) cameras
will facilitate this process where the Internet-protocol camera
is capable of accepting time synchronization input.
The industry accepted standard for time-synchronizing computers
and all digital data devices is the network-time protocol (NTP).
It is an open standard sponsored by the Internet Engineering Task
Force (IETF) and is defined by RFC1305. This standard specifies
an accuracy level of the time synchronizing device called the
Stratum level. The simple network-time protocol (SNTP) is another
such standard. With the proliferation of global positioning satellite
(GPS)-based timing equipment, these time references are readily
available for low cost. The use of an industry standard time-synchronization
protocol is recommended.
6. Recording Systems
Recording systems used in CCTV systems should adhere to the following
6.1. Recording Resolution for Analog Recording Systems
Analog VCRs must record each image at a minimum line resolution
of 240 visible lines. This resolution is typical of most VHS VCRs.
The use of VCRs with higher line resolutions (e.g., S-VHS VCRs and
tapes) is strongly encouraged because this improves image quality.
6.2. Recording Resolution for Digital Video Recorders
The minimum resolution requirements for DVRs will vary depending
on the media used to record the images. Some manufacturers quote
digital resolution (pixels) in analog lines of resolution. For rough
comparative purposes, a minimum digital resolution of 450 lines
can be used for DVRs using digital video tape. Digital video recorders
using a hard disk or optical disk for storage must record each frame
at a minimum resolution of 640 pixels in the horizontal direction
and 480 pixels in the vertical direction. (Differences in the units
used to describe these resolution recommendations are due to the
differences in the industry standards used to describe these media.)
If images are recorded in field mode, then each field must be recorded
at a minimum resolution of 640 by 240.
The Scientific Working Group on Imaging Technology strongly encourages
the use of higher resolutions than those described above whenever
Compression is a process in which the size of a digital file is
reduced. Due to the large amount of information present in each
second of video, most digital video systems use compression to reduce
storage and transmission requirements.
Compression may be lossless or lossy. In lossless compression, information
is not lost. In lossy compression, information is lost. If a file
has only been saved using lossy compression, then it is not possible
to recover all of the information in the original file.
In the event of an alarm-triggered mode (see Section 6.8), it is
recommended that lossless compression be used to record the sequence
of interest, if possible. If a system is incapable of lossless compression
during the alarm mode (as well as at all other times), then in order
to maximize the amount of information available to law enforcement,
it is strongly recommended that the lowest possible amount of compression
be used in recording files.
Some manufacturers use proprietary compression formats that require
the use of proprietary software in order to view the video sequences
or images. Use of such software can prevent or hinder law enforcement
from viewing or otherwise accessing these images. If such software
is used, then steps must be taken to ensure that law enforcement
will be able to access them when needed. See Section 11, Evidence
Handling, for more guidance.
6.4. Time-Lapse Recordings
NTSC (National Television Systems Committee) video records images
at a rate of approximately 30 frames per second. Each frame consists
of two fields or images, producing an actual rate of 60 images per
Analog videotapes are usually recorded in one of three speeds: standard
play (SP), long play (LP), or extended play/super-long play (EP/SLP).
A T-120 tape recording at SP speed will record for a period of two
hours, whereas a T-120 tape recording at LP speed will record for
a period of four hours, and a T-120 tape recording at EP/SLP speed
will record for a period of six hours. Changing the recording speed
from SP to LP to EP/SLP does not change the rate at which images
are recorded, it remains 60 images (fields) per second. Any recording
made at a rate of 60 fields per second is commonly referred to as
a real-time recording.
Time-lapse recorders are capable of recording video at rates that
are much lower than 60 images per second. This enables the recording
of images over a longer period of time. For example, using T-120
tapes, a VCR set in SP mode will record 30 frames (60 images) per
second for two hours. With a time-lapse setting of 24-hours, a T-120
tape will run for 12 times the normal two-hour tape length, and
the VCR will record no more than five images per second. Table 1
provides the image-recording rate for a variety of common time-lapse
settings under normal recording conditions.
Table 1. Typical Image Recording
Rate for Different
(Based on an approximate real-time rate of
60 fields per second.)
|Time-lapse mode (in hours)
|Number of fields (images)
(5 every 2 s)
(5 every 3 s)
(1 every 2 s)
Some analog time-lapse video recorders manufactured specifically
for CCTV security applications are designed to record a higher
number of fields per second in different time-lapse modes than
those reported in Table 1. For example, some high-density video
recorders can achieve record rates of more than 20 fields per
second in 24-hour time-lapse mode. Likewise, DVRs may also be
capable of recording at higher rates.
In order to meet the Scientific Working Group on Imaging Technology
guidelines, CCTV systems must capture and record at least one
complete field per camera per second. Any rate lower than this
may result in inadequate temporal coverage of events in the scene.
Facilities with more than one camera may choose to use a device
that enables the recording of images from all of the cameras to
a single recorder. The two most common devices used to do this
are switchers and multiplexers.
Switchers, as the name implies, alternate among multiple cameras
so that the output of the switcher at any one time is the signal
from a single camera. Systems in which the output of a switcher
serves as the input to the recording device will record images
from each camera in succession. The time that it takes for a switcher
to return to the same camera is called the camera interval. The
reciprocal of this interval is referred to as the camera refresh
rate. Therefore, a camera interval of one-half second would correspond
to a camera refresh rate of two times per second.
A multiplexer takes the outputs from multiple cameras and adds
an encoded signal that allows a picture from each camera to be
viewed in succession (as with switchers) or simultaneously. The
encoded signal is almost always vendor-proprietary, making it
difficult to recover the recorded images without the proper hardware
Switchers, multiplexers, and similar devices are frequently used
to generate multiimage displays. Multiimage displays consist of
a split screen that allows for the viewing of more than one camera
image on the screen simultaneously. Recording images in this mode,
however, significantly decreases the individual camera's image
size and quality. Many brands of duplex multiplexers will allow
the user to view multiple camera images simultaneously, while
still recording full-sized images from each camera.
In order to meet the Scientific Working Group on Imaging Technology
guidelines, CCTV systems must not record in multiimage modes.
Given the requirement in Section 6.4 that recordings capture at
least one complete field per camera per second, this will restrict
the refresh rate for each camera in a system with one recorder.
As a reference, Table 2 relates the number of images per second
per camera for given time-lapse recording modes.
Table 2. Typical Image Recording
Rate for Different
|Images (Fields) Recorded
per Second by Each Camera
||Time-Lapse Recording Mode (in hours)
|* Indicates limits fixed by the Scientific
Working Group on Imaging Technology requirement of one image
per camera per second.
|^ Indicates this cannot meet the Scientific
Working Group on Imaging Technology requirement of one image
per camera per second.
The values reported in Table 2 assume a nominal real-time recording
rate of 60 fields per second. As described in Section 6.4, some
CCTV security system video recorders designed specifically for
time-lapse applications are capable of exceeding the values reported
in this table. Under such circumstances, it will be possible to
record images from more cameras while still meeting the Scientific
Working Group on Imaging Technology requirement of one image per
camera per second.
6.6. Triggers/Incident Recorders
In some situations, systems may include triggers that lead to
the recording of images at a rate, or in a sequence, that differs
from the normal operating mode. An example of this would be to
change from time-lapse mode to real-time mode when triggered by
an alarm button. Another example would be to include an otherwise
inactive camera in the recorded sequence if motion was detected
in the field-of-view of that camera.
If such a device is used, its use must not conflict with the recommendation
in Section 6.4 (i.e., one field per second from every camera in
the system must continue to be recorded at a minimum).
Furthermore, test recordings should be made to ensure that activation
of the trigger and subsequent operation of the incident recorder
does not have a deleterious effect on the quality of the recorded
6.7. Remote Recording
Some CCTV systems transmit the system signal (images and other
information) to a remote site for recording.
The images transmitted this way are usually compressed significantly
in order to meet bandwidth restrictions. As noted in Section 6.3,
excessive compression severely degrades image quality.
In those situations in which remote monitoring is practiced, the
Scientific Working Group on Imaging Technology strongly recommends
that recording devices also be installed at each monitored location
so that images may be stored with a minimum of image compression,
In some cases, a remote facility recording video signals from
multiple off-site locations may also have the capability to control
recording devices installed at each off-site location. It is important
to ensure that this capability be tested on a regularly scheduled
basis. Procedures must be established that define the response
by personnel at the remote facility in the event of an incident
at one of the off-site locations. Steps should be taken to preserve
the recorded video at both the remote facility, as well as the
6.8. Alarm-Triggered Digital Buffers
In an alarm-activation event, law enforcement will seek to have
the highest possible image quality. This includes recording images
using lossless compression.
Therefore, in order to meet the Scientific Working Group on Imaging
Technology guidelines, CCTV systems that record images using lossy
compression must have an alarm-mode included in their system.
Furthermore, in the event of an alarm trigger in order to meet
the Scientific Working Group on Imaging Technology guidelines,
the following system settings are required for the alarm sequence:
- Lossless compression.
- The recorder must have a buffer capable of retaining the five
minutes of data prior to the alarm trigger using lossless compression.
- The system records at a rate of 60 fields per second, while
maintaining the same rate at which the system switches between
cameras (i.e., more pictures per camera each second if time-lapse
mode is normally used).
- Once triggered, the system should continue to record in a
lossless manner until manually stopped by an authorized agent,
according to the facility's policies and procedures. (Systems
should be configured to stop recording in the event that the
recorder runs out of memory or storage space prior to user intervention
in order to retain the existing images.) This period of time
should extend for at least five minutes after the completion
of the crime or event that led to the alarm. The recorder shall
have sufficient storage to be capable of recording in this mode
for a minimum of 30 minutes.
- All alarm data may be stored as black-and-white images.
Currently installed systems that are incapable of lossless compression
should be configured to record the alarm sequence at the lowest
possible compression ratio.
6.9. Digital Recorder Output Devices
Digital recording systems that do not use removable media for
day-to-day storage must be capable of exporting exact duplicates
of their recordings to removable media in a standard commercial
format. This is necessary so that law enforcement officials can
obtain copies of the recorded digital files that are a bit-for-bit
copy of the files stored on the system.
In order to meet the Scientific Working Group on Imaging Technology
guidelines, CCTV systems using digital recorders must be configured
to permit output to write-once storage devices including CD-WORM
(compact disc-write once read many times). It is strongly recommended
that systems also be configured to permit output to DVD (digital
versatile disk). This latter recommendation is based on the observation
that the recording of any alarm-triggered event will be over ten
minutes in length (five minutes before the alarm, plus the duration
of the event, plus five minutes after the event). The greater
storage capability of DVDs will reduce the number of disks needed
to store the recording on removable media. Systems designed to
output to DVD should not use standard compression techniques used
in the production of consumer DVDs (that is typically on the order
of 5:1) but should be capable of making bit-for-bit copies of
files recorded on the system hard drive(s).
6.10. Output File Types
Digital recording systems must be capable of exporting exact
duplicates of their digital image files to removable media. If
a system uses a proprietary format to store images, then steps
must be taken to ensure that law enforcement can extract an exact
copy of each image in the recording in a lossless and open file
format capable of fully supporting the recorded data. The current
preferred file format for such applications is TIFF.
Furthermore, in order to assist law enforcement in the expeditious
dissemination of still images immediately after an event, digital
recording systems must be capable of directly exporting still
images at the highest quality setting in one of the following
industry standard formats: TIFF, BMP, or JFIF (which commonly
uses the JPG extension). The ability to export to an uncompressed,
nonproprietary AVI (audio-video interleave) file and the native
video file format, in addition to one of the previously mentioned
still image formats, is desirable as well. All output formats
must maintain accurate aspect ratios consistent with the original
link to Part 2.