In today’s market, virtually every manufacturer in the industry seems to offer a DVR which is septaplex, octaplex or just plain complex! The bottom has fallen out of the recording market to such an extent that the basic DVR is now actually cheaper than the multiplexer and VCR. At the same time, the industry is swamped with talk of the imminent arrival of total IP solutions. But, in many cases, the infrastructure is not available to fully implement such systems.
Replacing the function of a multiplexer and VCR, the DVR is basically a computer that converts an incoming analogue signal from the cameras to digital, compresses it and stores it. With several video-compression standards to choose from, NVR-based systems rely on a message to be sent to the camera before a video signal can be obtained. The DVR is often placed at a central point, where the analogue feeds are terminated. Conversely, the NVR can be placed anywhere on the network. This may seem to be a disadvantage of the DVR, but as we shall see later, this is not necessarily the case.
Expressions like video over IP, IP server, network transmission and bandwidths may be on everyone’s lips, and security systems and network systems are undoubtedly merging more and more. But the immediate future is one of hybrid systems rather than pure IP solutions, and in such circumstances, a flexible DVR may provide a more suitable interim solution. Having said that, it is true that it is easier to implement NVRs on brand new installations than existing ones, and it is this sector of the market that is likely to lead the IP revolution.
Many end users are looking to integrate recording systems into complex networks, with remote configuration, remote control and central alarm switching from decentralised recordings becoming increasingly important.
In order to help carry out their surveillance duties more effectively, large-security system users should also have at their disposal both analogue components, such as a keyboard, joystick and jog shuttle, as well as digital operating tools, such as graphical user interfaces or digitised site plans.
To achieve this, the conventional analogue matrix is being superseded by a modern digital matrix – a facility that is offered by both approaches. The digital matrix’s crucial advantage lies in its flexibility, supporting as it does a variety of levels of integration with, and entry into, the digital world. This provides remote control access to all networked recorders and live and archived pictures.
DVR strengths
So we’ve seen how the DVR still has a role in relation to the current trend for hybrid solutions, but what are its other strengths? Well firstly, it has built-in playback tools and slow motion – each with various different speed settings – or single-frame replay forwards and backwards to enable accurate picture analysis. Fast, easy-to-use and highly accurate picture review techniques are especially needed for monitoring tasks, where crucial details need to be spotted despite quick movements and actions. One example is the monitoring of hand movements when chips are being positioned and items are being counted in casino games.
Using encoders/decoders, the DVR can act as both a transmission and recording device. Decoded data can be displayed directly onto a linked video monitor. In parallel, video footage can be recorded digitally, called up and transmitted over an Ethernet/IP network.
Management software on the PC also enables easy control of virtual matrix functions. Each camera and each recording can be switched to the display monitor. Thanks to decentralised recording and efficient multicast streaming, the system does not make large demands on bandwidth, allowing several control rooms to operate at the same time. Software also supports data export (back-up) and the synchronous replay of several camera recordings (group playback).
With local recording, the DVR also offers redundancy in the system. So, if one of the video hard disks fails, the data is still retained on the other disks. Both video streaming and video recording continue to function, and this is enhanced when the operating system is held on flash memory, enabling removable hard disks if required.
Using a loop-back option enables the displayed video signal in the decoder to be recorded as well. This can be used as both an additional check and for system redundancy. For example, if all the disks in the encoder fail, then the DVR is still in the position to stream the video signal over the network. If this encoder is then switched to a decoder and loop-back is used to record, then you can produce a complete remote recording of the desired video source.
The construction of centralised recording systems is also possible, as encoders are able to work without a hard disk and transmit a video data stream over the network. Data from the DVR is stored on a so-called NAS (Network Attached Storage) file server in the network, with images accessed from a central management workstation. One drawback of this approach, however, are the very high demands on the network and the file server. Consequently, if there is a large number of cameras, the decentralised solution is likely to be safer and more economical. And while the ability of NVRs to route out different transmission paths in the event of a failure is seen as a key selling point, we are still waiting for a reliable and cost-effective infrastructure to facilitate this.
Choice of compressions
Combining different compression types has also prolonged the lifespan of the DVR, by providing added flexibility for the end user. Some systems offer Wavelet technology, which has the advantage of delivering excellent picture quality, with images watermarked for authenticity. The Kalagate Institute tests such systems and approves the pictures for use in European courts.
MPEG-2 currently offers high performance in full PAL resolution for real-time applications, but many current MPEG-4 hardware solutions only use the MPEG-4 Simple Profile and represent a compromise between resolutions, picture refresh rate and picture quality. Consequently, DVR manufacturers offering the highest quality solutions will tend not to use MPEG-4 as a recording compression, because for real-time applications, the same or even a higher data rate than MPEG-2 is needed. Unfortunately, this is often overlooked in the marketing hype.
MPEG-4 part 10, also called MPEG-4 AVC (Advanced Video Coding), however, offers significantly better compression. It supports DVD video with less than 40% of the bit rate of MPEG-2 and will be used as the future standard for high-resolution digital TV, TV via ADSL and the Blue Laser HD DVD.
DVRs are now also offering the ITU-TH.264 standard (H.264), which arose from co-operation between the ITU-TH.26L (or H.263++) and the ISO-MPEG, and complies with ISO Standard MPEG-4 Part 10 or MPEG-4 AVC. This compression facilitates real-time split displays, real-time recording for multiple channels, synchronised recorded audio for all channels and virtual matrix functionality.
There are many compressions currently available, but ultimately, it is the relevant customer benefit and application scenario that is most important. That being the case, manufacturers are moving to support all the common standards in the market, so that they are able to select the most suitable process for a client.
Conclusion
Forward-thinking companies should be offering products that can be adapted as a user’s infrastructure grows. So taking a modular approach benefits end users and allows them to realise the greatest potential. In many cases, the best solution currently has to be a hybrid DVR, which offers the facility to have analogue and IP video inputs, local redundant recording, the ability to stream video on demand, integration into a virtual digital matrix and the option of centralised recording.
The DVR is far from dead, but the end user has to distinguish between products that are cheap and limited, and those that are flexible enough to be integrated into any system.
Oliver Vellacott highlights the differences between digital video recorders and network video recorders, and explains why the latter will deliver a knockout blow.
The rapid development of video compression algorithms (JPEG, MJPEG, MPEG-4 etc.), computer processing speeds and a rapid reduction in data storage costs. These were the precursors which gave rise to the DVR – a device you could consider as being the function of a multiplexer, together with a computer disk for storage in place of tape, all housed in the same box with some additional ports for connectivity.
The DVR provides a convenient, if limited, replacement for the multiplexer and VCR combination and provides non-linear access to recorded material usually selected by camera ID, time and date. In general, the consistency of quality of recorded material will be higher than that obtained with analogue tape, although the actual quality achieved may or may not be better, depending on the compression algorithm and individual configuration.
In general more programmable options for individual video stream recording parameters – picture resolution, number of frames per second, trigger options, start/stop times etc – are available, but a DVR is only useful where the analogue cameras are all cabled back to the DVR’s location. Competent DVRs now feature UDP (CAT 5) network ports, so that the device can be provided with an IP address and thereby become accessible over an Ethernet network. Many limitations still apply, however, not the least of which being that if it fails you’ll probably lose all your recordings.
If you are going to use a DVR make sure that the one you’re proposing incorporates an industrial grade hard disk drive (HDD). Most DVR failures arise from overworked and overheated hard drives. And like most other things in this world, the actual performance obtained from a DVR, its ease of use and reliability, will depend upon the manufacturer, individual model selected and price paid.
A natural successor
The network video recorder heralds the arrival of the next natural point in the development of recording technology. It is important, however, to differentiate between DVRs and NVRs, as both are often termed ‘digital’.
A DVR digitally compresses analogue video feeds and stores them on a hard drive – the term ‘digital’ referring to the compression and storage technology, not the transmitted video images. The DVR therefore has to be located near the analogue feeds. In contrast, an NVR stores digital images directly from the IP network. Therefore, the most obvious difference between the DVR and NVR is that whereas the DVR records from analogue streams provided from analogue cameras, the NVR records video streams that have already been encoded at the cameras. So there are no video connectors anywhere on a NVR; its input and output is IP data, comprising compressed and encoded video. This will typically be in MPEG-4 format, which has enjoyed widespread adoption in the CCTV industry as the current compression technology of choice.
The huge advantage of architecture based on NVRs is that they can be located anywhere on a network – for example, at the monitoring centre, adjacent to camera clusters, on the edge of a network, or collected together in a hardened environment. When in use their location is transparent to an operator – he or she simply calls up the recorded video stream to be viewed and, provided that they have the necessary authorisation, it is readily available. NVRs record and replay simultaneously, and recordings on any one machine can be remotely viewed by a number of authorised operators spread across the network simultaneously, all totally independently and without affecting each other.
Location location
The importance of the independence of physical location, well away from the cameras if necessary, should not be underestimated; IT managers are notoriously zealous in safeguarding their network capacity and rightly so, but by calculating the data flow requirement across the network and strategically placing NVRs accordingly, the impact of video streaming on bandwidth usage can be minimised. Typically, an NVR might be placed on a local area network (LAN) and near, in network terms, to a camera cluster. This ensures that the load is carried by a LAN capable of absorbing it easily, thus saving capacity on other, perhaps more restricted, parts of the network. The IT manager can specify what level of bandwidth he is prepared to make available for video streaming. This can be set as a cap, so that it is not exceeded.
When a recording is required at any other point on the network, it can be called up seamlessly by the operator, streamed, analysed, viewed and acted upon accordingly. To assist in the calculation of data flow and disk storage capacity requirements, spreadsheet-based calculators are available, enabling these numbers to be calculated on a camera-by-camera basis using certain parameters. These could include the scene type (a busy street, internal corridor etc), functionality of the camera (PTZ under continuous operator control / static for ID purposes etc), picture resolution and update rate in frames-per-second, and if motion-sensing is used, the motion frequency and type.
Competent NVRs now embody features such as:
- Hot-swappable disks;
- Simple Network Management Protocol (SNMP) support;
- Built-in diagnostics;
- Protection of files against deletion;
- In-built firewall for the protection of data;
- File export function, which embodies the watermarking and digital signature based on individual video frames and audit trail;
- Synchronised audio and video recording and playback;
- Hard-disk temperature monitoring;
- Dual, fully-redundant power supplies and network connections, (the latter providing uninterrupted and continued operation in the event of a single power supply or network failure).
On the subject of reliability, mirroring techniques are now often used to duplicate the recording of video streams on additional NVRs located at different parts of the network. This provides a high level of protection against network failure because if one part goes down the other is there as a back-up.
Scalability is a further advantage of the NVR. Indeed, adding another device is just a matter of plugging it in and configuring it. In addition, there is no requirement for further video cabling. This is a real benefit when consolidating several independent systems into one managed environment, or in system rationalisation or expansion, as it removes all of the cost associated with re-cabling.
Activity Controlled Framerate (ACF) is also used to reduce the size, and hence the cost, of disks. This facility relies on processing at the camera encoder. When in use, if no movement is detected in the camera scene, then the recorder falls back to a low recording rate – typically one frame per second. However, when movement is detected in the scene, it returns to its pre-programmed recording rate, achieving this in typically only 100ms. This feature is most effective in places where low activity occurs, such as in corridors or on fire escapes, or internally in buildings which are unoccupied at night. It can save as much as 50% of the disk storage capacity that would otherwise be required.
A software future?
Many tools are already available to assist the operator in identifying and replaying events of interest from a recording. Software can, for example, analyse movement in a scene and display thumbnails on the screen that represent frames from recordings containing the specified movement. Clicking on one of the thumbnails then replays that section of video. Systems can search 24 hours of recorded video and display these thumbnails in just a few seconds.
Analytics software and fast and efficient image searching techniques not only benefit the user; they also help to reduce the overall demand on the network. But this is just the tip of the iceberg – new developments encompass, for example, congestion detection, advanced motion detection, abandoned object detection, counter flow, virtual tripwire, object tracking and theft detection. It can be expected that huge productivity improvements will result from using analytics software during the searching of recorded material in post-event analysis. And for this reason alone, the NVR holds all the cards.