A digital video recording system transmits and compresses the camera’s analog image signal to digital signal and monitors and records the camera’s image signals for long periods of time.
Unlike an analog videotape recording system (VCR), a digital video recording system (DVR) converts an analog video to a digital stream and saves it into a hard drive (HDD) after it is compressed.
The shift from analog to digital DVR technology in surveillance is mirrored by several other major shifts in security technology, such as the trend away from single input to multiple input, from local area control to wide area remote networked control, and from b/w to colour accompanied by higher resolution. More advanced image compression technology is stretching recorded image durations and narrow band transmission is moving to broadband. Increased computer processing power and expanding hard drive size enable previously offline processing to be done in realtime and faster searching of image data. Furthermore, digital watermarking technology allows for confirmation of the authenticity of stored images.
The market positioning of DVR products is determined by the particular strengths and weaknesses of the compression standards they use. It is highly probable that MPEG-2/MPEG-4 and JPEG-2000 will prevail in the security industry in the medium-term future. No doubt, more and more people are moving to digital based CCTV systems over the conventional analog VCR-based systems.
Benefits of digital systems
* Access and control can be done from several locations.
* System is automated - one does not have to swap or replace VCR tapes thus allowing minimum intervention.
* The system can record for several weeks - depending on the size of the hard drives.
* A digital system allows the user to instantly retrieve relevant data.
* Data is stored in a database which can be searched by camera, time, date and motion. This saves the user valuable time in identifying the target or incidence.
* Images can be replayed over and over again without deterioration.
* Flexibility of recording modes - schedule (ie, time and date), alarm activation and smart motion detection.
Technical trends of DVR
Trends of 2002:
* Continuous price competition.
* Low price PC-based DVR and low-end embedded DVR.
* Continuous increasing of recording speed and image resolution.
* PC-based DVR: 60~240 fps, Embedded DVR: 30~180 fps.
* 640x480 or 768x576 resolution becomes realistic.
* New compressions are introduced MPEG-2&4, differential Wavelet.
Trends for 2003:
* Mobile surveillance by wireless LAN or modem with PDA.
* Introduction of video noise reduction.
* Product portfolio compatibility.
* Integration across multiple platforms.
* True DVD recording.
* Enhanced MPEG 1.
* Enhanced MPEG 2 hardware - ASIC chip.
* Triplex on remote.
* Up to 480 fps recording.
* Highly efficient synchronised voice recording.
* Compatibility across full family line.
* Cross compatibility.
* Noise discrimination.
* Search on server and remote.
DVR selection methods
1. Prerequisites for selecting a surveillance device is:
* Stability - no bugs.
* Automatic recovery function in time of system abnormality.
* Notification function to administrator in time of system abnormality.
* Need protective circuit in image process board.
2. Standard of DVR comparison by manufacturing companies:
* Stability (each certification, durability, CPU load state, etc,) need to be guaranteed.
* Recording speed - fast.
* Recording screen quality - superior.
* Surveillance - realtime need to be possible.
* Speed of remote image transmission need to be fast.
* Operation need to be simple.
* Size of recorded file need to be small. Number of recorded days will decrease with larger compression size.
* Digital watermarking.
* Each function needs to be diverse and embodied simultaneously. (Audio recording, automatic movement tracking, MAP function, etc).
In most countries digital data is not legally supported in the courts due to its high susceptibility to being edited and modified by any users in various ways and places, and that has been the major concern when users adopt DVR. For example, banking is still very conservative toward digital recording and less likely than government bodies or gambling establishments to upgrade their systems with new digital products, even though it is a big adherent of surveillance products.
The malicious tampering of recorded DVR data in a criminal trial can result in either a wrong conviction or acquittal. Therefore, an image and video authentication system for the prevention of forgery and the unauthorised alteration is needed aside from the purchase of higher quality digital recording equipment. Recently, copyright protection technologies have been rapidly improved by digital signal processing methods. One such copyright protection technology is a digital watermarking system.
This system embeds additional information into the original multimedia data to protect against the illegal copying and manipulation of the data. Also an encryption technology is becoming a very popular method to keep the information secure. Usually the DVR systems use both technologies for improving their properties. The problem of an encryption technology is that it is unable to protect data after decryption. However, digital watermarking, ie, embedding the watermark into the original un-encrypted multimedia content, can protect the data even if the data is encrypted or decrypted.
The illegally modified content would be detected after authentication checking via a digital watermarking technology.
Since the DVR manufacturers have solved the legal problem of digital multimedia resources, the DVR system with digital watermarking is one of the total security solutions and will include more intelligent security functions in the future.
For more information contact Abie Ali, Frank Street, 011 838 4515.
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