CCTV Technical Information and Guidance
Topic Covered on this pageCCTV Recording
CCTV Image Rates
CCTV Image Rate Definition
CCTV Recording Duration
CCTV Data Export & Remote Playback Capability
CCTV Playback and Software
CCTV Recordings
It should be noted that all Data Protection, HOSDB and ICO requirements and guidelines should be adhered to when recording CCTV images.
When installing or upgrading a CCTV system consideration should be given to the recording of CCTV Images. There are basically two types available. Analogue use either VHS or SVHS tapes as the storage medium or digital with an internal hard drive or removable DVD discs.
New CCTV systems will typically have Digital Video Recorders (DVR). These generally should be fitted with removable hard drive memory units, designed for easy removal without the need for specialist engineering or technical support.
RAID (Redundant Array of Independent Discs) array recording systems are not recommended as they create difficulties when exporting large volumes of recorded video, often the only alternative is to remove the whole raid array system.
RAID is defined as a method of recording CCTV images across multiple drives; a number of hard drives are connected into one large segmented mass storage device. There is RAID-0 to RAID 5 systems. This method can offer improved fault tolerance and enhanced quality of data over a single hard drive or group of independent hard drives. However, it may be more difficult to retrieve evidence into a single image for viewing purposes.)
The majority of DVRs are feature rich providing both recording and playback facilities with variable operational controls.
Digital systems must be capable of providing usable images / evidence for use by the police and courts. Exported images shall be capable of being immediately viewed on any contemporary MS Windows operating system without the need for proprietary software to be installed i.e. the playback software and video files should be capable of running from the exported disk.
The recording period is recommended for both analogue and digital systems is 31 days storage before the recorded data is overwritten, the number of connected cameras, record rate and quality will determine the drive size.
CCTV Image Rates
With most systems a broadcast quality of 25 ipspc can be captured. This is a high image rate giving the appearance of smoothly flowing motion and is more than adequate for most scenarios. However, in order to reduce the amount of video data that needs to be stored, CCTV systems can allow this figure (ipspc) to be reduced.
Whilst broadcast quality video is recorded at 25 ipspc most commercial security and operational CCTV images are recorded between 5 and 12.5 ipspc (medium image rate). At 12.5 ipspc it is unlikely that the difference between this and broadcast images will be noticeable if target speed is high or the scene is complex then a medium or high image rate is advised (more than 5 ipspc). A reduction in image rate could reduce the storage size but will also compromise the clarity and detail of the images being recorded. For example with a “one under” will the selected image rate capture if the individual was pushed, fell or jumped?
The recorded image rate will always be a compromise with recorded storage size and retention period. It is recommended you consult with your CCTV systems provider at the design stage to ensure the system will meet your individual requirement. A popular way of utilising the storage space of a recorder is to record at a low image rate, say below 5 ipspc, but to increase the image rate, say 12.5 ipspc, if an alarm on the system is triggered.
CCTV Image Rate Definition
For the purposes of this document image rate is defined as shown below:
High image rate is 12.5 to 25 ipspc (plus)
Medium image rate is 5 to 12.5 ipspc
Low image rate is below 5 ipspc
CCTV Recording Duration
The ACPO/Home Office National CCTV Strategy document issued in October 2007 recommend that recordings be retained for 31 days to support both major crime investigation and counter-terrorist measures.
CCTV Data Export & Remote Playback Capability
Data Export means the removal of data from the recorder to another device or disc.
Data Seizure means the removal of the recording devise (unit or complete drive) from its normal location to an alternative location. Systems should be designed to allow operators/authorised persons to export CCTV Images of incidents from the recorder onto an appropriate storage media for removal from site to another location for viewing.
The appropriate processes and procedures should be in place to ensure the daily download of CCTV images and download of CCTV Images for major incidents are fully understood by all staff operating the CCTV equipment .
Modern CCTV systems rely on digital recording technology and these new methods present their own problems. With video tapes it was very easy to remove a tape and give it to the law enforcement agencies such as the police for use as part of an investigation. It is important that your images can be used by appropriate law enforcement agencies if this is envisaged. If they cannot, this may undermine the purpose for undertaking CCTV surveillance. System operators should put in place arrangements with the police so that images may be routinely exported in a timely fashion.
The data export system should allow exporting on to other media – including still and other suitable storage media (e.g. DVD, HDD) or SVHS, VHS tapes in the case of analogue systems and should include the software necessary for playback and exporting. All propriety software, required for remote playback, should be exported onto the recorded media.
The exported data should be such that it allows stills and composites to be produced in line with the requirements of the criminal justice system. Please refer to HOSDB document “Digital Imaging Procedure” version 2.0. Single and/or multi-camera exports should be possible at all times.
When specifying a system, consideration should be given to the maximum acceptable time for exporting CCTV images. It is suggested that this be specified in terms of the time taken to transfer images of all cameras from the recorder to the selected export media for a time period of two hours.
Large or High Profile organisations should consider the need for the authorities to seize the recording equipment or elements of it, such as the HDD. To ensure any business remains fully operational from a CCTV monitoring and recording perspective, should a major seizure occur, it is strongly recommended a risk assessment is conducted The security risk assessment will cover, but not limited to:-
The recommended spares held by the operator or their supplier will result from the outcome of the security risk assessments.
Systems and the associated operating procedures should have the capability to protect specific pictures or sequences, identified as relevant to an investigation, to prevent overwriting before an investigator can view or export them.
When exporting images it is essential that the information displayed on the recorded image, such as time, date and camera detail, is identical to that pertaining at the instant of recording the original live image. It is recommended that the time and date signals are generated by a common time source (Atomic Clock) to ensure synchronisation throughout the CCTV system.
In addition, it should be possible for an appropriate organisation (e.g. Policing Authorities, etc.) to playback images they have exported on a playback facility located away from the station or car park.
The recommended option is for the software necessary to view images to be included with the exported data. Alternatively, the supplier should make available any software needed to enable images to be viewed. Export of a system event log or audit trail and any system settings should be available along with the pictures to help establish the integrity of the images and system.
The replay software should allow the investigator to search the pictures quickly, effectively and see all the information contained in the picture and associated with it.
It should be possible to replay the exported files immediately i.e. without the need for re-indexing of files or verification checks.
The playback software should ideally: A Variable speed control, including fast forward and rewind and frame by frame forward and reverse viewing.
Be able to display single and multiple cameras and maintain aspect ratio.
Allow the recording from each camera to be searched by time and date.
Permit printing and/or saving (e.g. .bmp) of individual pictures with time and date.
Show a single camera at full resolution.
Data export systems should be networked so that an investigator can remotely view and export events directly from the data store.
At the time of designing a new or modified CCTV system consideration should be given to the fact there is an aspiration to monitor live images and export recorded images at a remote location such as a head office or a 3rd party control centre.
CCTV Playback and Software
It should be possible for operators / authorised persons to playback recorded images of both a minor and major nature, from any camera based system own playback facility.
The replay software should allow the reviewer to search the pictures effectively and see all the information contained in the picture and associated with it.
The playback software should:
have variable speed control, including fast forward and rewind and frame by frame forward and reverse viewing
display single and multiple cameras and maintain aspect ratio
permit the recording from each camera to be searched by time and date;
allow printing and/or saving (e.g. .bmp) of pictures with time and date;
- display a single camera at full resolution.
When playing back images it is essential that the information displayed on the recorded image, such as time, date and camera detail, is identical to that pertaining at the instant of recording the original live image. It is recommended that the time and date signals are generated by a common time source (Atomic Clock) to ensure synchronisation throughout the CCTV system