Video and audio recording

CCTV systems based on analog cameras can store video (and audio) on standalone digital video recorders (DVRs)

The images from analog cameras recorded on the DVR can be viewed over the Internet

IP CCTV systems store digital video (and audio) streams on:

An IP CCTV systems based on Sunell cameras with local recording on microSDXC cards

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In the case of migration from analog to IP CCTV system, modern DVRs can be included into the new system, cooperating with NVRs. Such a system can be managed by VMS software. Ultimax/Hikvision DVRs can also work as video servers providing RTSP streams.

Systems which record video signal in compressed digital form are nowadays the basic platform of video archiving, offering numerous advantages connected with storing and transmitting the information.

Digital recordings as evidence in courts

There is no strict definition what form of video recording can be used as material evidence. The court evaluates the importance of the recordings, usually based on opinion of experts.

Image detail is classified into four categories based on the number of pixels used to represent an object with height of 50 cm:

The categories allow for:

CCTV systems usually record images from individual cameras at frame rates from several to 25/30 frames per second (fps). The total capacity of a DVR (from all cameras) can reach hundreds of fps (e.g. Ultimax 1316 M72316 – 400 fps).

Obviously, the number of channels and their recording modes, frame rates, image resolutions, compression ratios and some other parameters have direct effect on the required size of the disk space for a given retention time. The retention time is often evaluated for the maximum load, i.e. continuous recording of images of best quality at the highest frame rate. For example, after installing eight 3TB SATA HDDs in DL-8516 H.264 M78516 DVR, the total capacity of 24TB will be sufficient for archiving 4CIF video in continuous recording mode from 16 channels at frame rate of 25 fps for over 50 days.

Motion detection allows for a much better management of storage resources. In this mode, the video from the camera is recorded only when something happens in the scene. This function significantly extends the retention time. Video motion detection is available in almost all DVRs. Typically, the user can define the areas (zones) of motion detection and its sensitivity.

The motion detection events create indexes of the recordings, which makes it easier to find the relevant video files.

Simultaneous recording and playback

A particularly useful feature of digital systems is their ability of simultaneous recording and playback, yet after ten or so seconds from the start of recording. Sometimes it is also possible to search a fragment of the recorded video sequence with some characteristic features, e.g. motion detection, lighting change, zone intrusion. That feature is unavailable for analog systems. As the result of that search, we receive a set of images fulfilling the criteria, and it can be done without interrupting the recording process (triplex DVRs). It is also possible to use digital zoom function to enlarge the image, even up to 16 times. Unfortunately, it doesn't make resolution higher, anyway the use of filters reducing noise and increasing sharpness simulates resolution improvement in a sense. Next advantages of digital systems are quick configuration of alarm mode and easy setup during normal operation mode.

Network connectivity

Practically every DVR has a built-in Ethernet card, which can be used to connect several devices together or for online monitoring and playback. Other network functions include remote control of PTZ cameras, I/O devices etc.

We should note that most DVRs/NVRs do not allow to remove the HDD and install it in a normal PC, where the recorded video material can be reviewed. It is one of the methods used by the manufacturers to protect the original content. Another one is "watermark".
The copy of the data can be made via USB port (e.g. to a flash memory), or via LAN network, directly to a HDD of a PC. The copied data can be played with popular multimedia players or with dedicated software (e.g. a file converter).

Recording parameters

Video and optionally audio data streams are recorded on hard drives (HDDs). The quality of video image transmitted to DVR/NVR should be good enough for the recording resolution, as digital recording doesn't improve the quality of input signals.

To fully use the recording parameters of a DVR/NVR, the resolutions of the images from cameras should be not lower than the recording resolutions of the DVR/NVR channels.

The second important parameter is recording speed, measured in frames per second (fps). It can be selected from the values declared by the DVR manufacturer. Higher frame rates require proportionally higher disk space.

The third issue, affecting the recording quality of video streams transmitted over IP networks, is bandwidth management. There are CBR (Constant Bit Rate) and VBR (Variable Bit Rate) options for the stream width. In the former case this parameter is set as a numerical value, in the latter case it is usually described by "image quality".

More about compression methods can be found here.

Alarm inputs and outputs

DVRs usually have the same number of alarm inputs as video inputs. The number of alarm outputs is normally lower, from one to four. Alarm inputs and outputs are used to connect CCTV systems with other security systems, mostly for fire and intrusion protection, and to trigger specific actions as responses to various events.

High-end DVRs/NVRs allow administrators to divide disks into basic (primary) and alarm partitions. During normal operation, such a device records the video on the primary partition, but when an alarm occurs, the recording is switched to the alarm partition. This feature guarantees that even when the DVR is in overwrite mode (overwriting the oldest recordings when the disk is full), the recordings of the important events will not be deleted, being saved on the separate partition. Removal of the data from the alarm partition is possible only after entering the password known by the administrator.

Access lock

Access to DVRs/NVRs is normally protected by passwords. Additionally, each digital system can be secured from recording data from unauthorized sources. It means that the stored video data cannot be modified on a PC and put back on the HDD in the system like it was from cameras. The security measures ensure that only data coming from cameras is recorded in the system resources. In order to increase the authenticity, the system adds data and time stamps to each frame.

The digital systems include:

Before choosing a recording system, the investor should take into account basic features of these solutions.

PC cards

PC cards offer advanced features at lowest prices, usually use the newest software, the systems based on the cards feature flexible configuration/reconfiguration and can be easily expanded in the future. Typical problems are connected with the right selection of hardware, software and additional security measures against unwanted modification performed by people or viruses. The intrusions into Windows are the reason of about 60% cases of improper operation of the systems (the other 40% are problems caused by wrong hardware selection and errors during configuration).

Specialized computers

In the case of computers with independent operating systems, there are no disadvantages related to hardware selection or software modifications - they are sold in the form of motherboards with operating system (mostly Linux) which only require to connect suitable power supply and HDD. They can be installed in standard PC housings, also together with already working computers (the cases have to be large enough, with powerful power supplies).

Standalone DVRs

Currently, DVRs are the most widespread devices for archiving images and sound from CCTV cameras. They offer preview and recording of video from up to 16 analog cameras at 4CIF resolution and 25 fps. They support schedule recording, privacy masking, PTZ control and have alarm inputs and outputs.

The HDDs installed in DVRs are formatted so that to make it impossible to manipulate the data. Both the DVR and video players examine this structure.

Archival material can be played back synchronously (simultaneously from multiple cameras) directly on the DVR, remotely via IP network, on a computer with a free application, or using a web browser. Selected parts of the recordings can also be copied onto flash drives (via USB) or the hard drive can be transferred to a PC using the free player application.

Transmission over IP networks can be performed with the use of two streams. The first (main) stream is the same which carries the video and audio recorded on the HDD. The parameters of the second (auxiliary) stream can be set independently from the first one (the bitrate may be much lower to enable Internet preview over slower networks).

Basic configuration of a Hikvision/Ultimax DVR (there are shown single devices only)

Network Video Recorders (NVRs)

NVRs are plug &play devices for managing IP CCTV systems. The main functions include live monitoring, recording of video streams, playback of the archives. NVR platform is very flexible and allows multi-server multi-client operation. NVRs have various numbers of channels, support different resolutions and recording speeds, differ in the maximum bandwidth per channel (and/or for the entire device - it often means interchangeability between the number of channels and their bandwidth), etc.
The flexibility of NVR-based systems is connected with operation in IP networks. Client stations can connect to any channels of the NVRs deployed anywhere in the network. The advantage of standalone NVRs is the fact that they can be located close to the cameras, which remarkably increases the reliability of the systems.
Some NVRs are equipped with VGA/HDMI outputs and other interfaces - such a device can be directly connected with a monitor, mouse, and keyboard. This eliminates the need for additional PC workstation for configuring the system.

Hybrid DVRs/NVRs

Hybrid DVRs/NVRs combine features of DVRs for analog cameras and NVRs for IP cameras. They are mostly based on Linux systems and enable the users to monitor and record images from the both kinds of CCTV cameras. The devices are chosen when the system should simultaneously use analog CCTV cameras and megapixel IP cameras. It is often the best solution, as most cameras in CCTV systems don't have to provide megapixel images and the video from analog cameras recorded at 4CIF resolution is fully satisfactory. The megapixel cameras are needed only in specific areas where they should ensure facial recognition and high image detail.

NVR software

Manufacturers of IP cameras include free software for monitoring and recording the video and sound. These applications typically provide simple recording and searching functionality.
Commercial video surveillance software has much more advanced functions. Choosing an NVR application, the user should pay special attention to the performance of the computers that will run the software. The software producers often specify configurations that are required for their products. The most important components are the motherboard, processor, video card. Some of these components are sometimes critical.

Commercial video surveillance software controls the largest and most responsible systems in the world. One of its main advantages is scalability. At the beginning, the user can buy a basic version for a small number of cameras, and freely expand the system according to the needs, buying additional licenses or more sophisticated versions in the future. However, it is important to note that with the increasing number of channels and the total bandwidth, the performance requirements for the PC hardware rise as well. So, it is recommended to use more powerful PC configurations at the start, to avoid replacement after such upgrades.