Selection of a multi-channel DVR
Video Recorder (DVR) - a device that allows you to easily and cheaply organize video surveillance.
In this article I will talk about the most common class - recorders working with analog video cameras. This recorder allows you to connect 4, 8 or 16 cameras, as well as 1 or more microphones. Recording is carried out on a hard disk that is installed inside the recorder. Most recorders are sold without hard drives. The disk is put usual computer with interface SATA. An analog monitor or TV, a VGA monitor can be connected to the recorder, some have an HDMI output. All modern recorders can connect to the local network and the Internet. It allows you to monitor, view records and manage the recorder from a computer and mobile devices.
Locally, the recorder is controlled by buttons on the front panel, an infrared remote control and a USB mouse.
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Video inputs and recorder outputs - BNC connectors, audio inputs and outputs - RCA (tulips).
The signal from the camcorder is a regular PAL composite video signal. Security camera can be connected to the video input of a regular TV. Microphone inputs are linear 200 mV, so microphones must have a built-in amplifier.
The DVR can record in three modes: manually (by pressing the "record" button), by schedule, by motion detector. Many recorders can also record a few seconds before the start of the movement and a few seconds after it ends.
And now, actually, about the choice.
1. The number of inputs.
As I wrote at the beginning, recorders come with 4, 8, and 16 video inputs (very rarely with 9 and 32 inputs). The audio inputs are usually either the same as the video inputs or one or none. Four-channel recorders are considered budget, so they are much cheaper than the rest with the best parameters. An ideal 4-channel recorder will cost about 4,000 rubles, while an 8-channel recorder will be 11,000 rubles at best, and a 16-channel recorder will cost 22,000 rubles. What is the catch of cheaper multi-channel recorders will tell below. Of course, any recorder does not require connecting cameras to all inputs. You can use a 4-channel recorder with a single camera.
2. Resolution and recording speed.
These are the main parameters of any registrar. Ideally, the recorder should write each channel at a speed of 25 frames per second (Realtime) and full resolution of PAL 720x576 (D1). In video surveillance adopted the following notation for the image:
960H - 960x576
D1 - 720x576
4CIF - 704x576
HD1 - 720x288
2CIF - 704x288
CIF - 352x288
QCIF - 176x144
Very often, DVRs indicate the recording speed for all channels simultaneously. For example, if the technical parameters of a cheap 16-channel recorder indicate “Record - 100k / s (D1)”, this means that each channel will be written at a speed of 100/16 = 6.25 frames per second. At the same time, the same recorder can write 400 frames per second (25 fps per channel), but at a low resolution of CIF. Some cheap recorders allow non-linear redistribution of recording speed between channels. For example, with a total recording speed of 100 fps, you can write two channels at a speed of 25 fps, and the remaining fourteen at a speed of 3.5 fps.
This is the secret of the price of cheap registrars. They have a low write speed in full resolution. Until now, there are recorders that generally can not work at full D1 resolution and support only CIF, which is only 352x288 pixels. And I also met Chinese recorders, in which the two channels had a full resolution of D1, and the rest - CIF.
With 4-channel recorders, everything is simple and clear - you need to take Realtime D1 (100 fps on 4 channels), because there are a lot of them and they cost from 3000 rubles.
With 8- and 16-channel everything is more complicated. Realtime is twice as expensive as a D1 recorder at a speed of 5 or 6 fps. Do I need a Realtime Record? By and large, the information content of video surveillance does not affect, 5 frames per second is shown or 25. But 25 of course is more pleasant to watch. But registrars writing D1 at a speed of 6 fps cost from 5,000 rubles for an 8-channel channel and from 9,500 for a 16-channel channel.
But it’s definitely not worth saving on recording resolution and the registrar must support recording in D1 (720x576) or 4CIF (704x576) format.
The vast majority of modern recorders use the H264 codec, which allows to compress video strongly without significant loss of quality. A 500-gigabyte disk can be enough for several weeks to record 16 channels of motion detection.
3. Convenience record settings.
It is desirable that the recorder adjusts the brightness, contrast and chroma of the image for each channel.
It is important that the motion detector works well in the recorder, because the recording by the detector simplifies the subsequent search and significantly increases the storage time of the records on the hard disk.
Pay attention to the pre-recording and post-recording settings. It is convenient when the recorder records a couple of seconds before the start of the movement and after its termination, but when these values ​​cannot be set less than 5 seconds before the start and 10 seconds after the end of the movement, this greatly hinders: for each event, you have to watch the extra 15 seconds.
4. Ease of searching and viewing.
Different registrars search and view are organized differently. It is convenient when each event can be viewed separately, but after its display the recorder does not stop, but shows the next event.
5. Ability to save the record in a convenient format.
All recorders allow you to save video clips and frames to a USB flash drive. Many registrars are able to save data over the network on a computer.
I met registrars who saved the video in its format that is not compatible with anything. It was proposed to watch these files using a special player program, and it was impossible to convert them to generally accepted formats.
It is desirable that the recorder can save video files in AVI format.
6. Networking.
It is convenient when you can view a live picture, record and manage the recorder from a computer. All modern recorders have network capabilities, but for all this is implemented in different ways:
The worst option is to work only from the browser, and the browser is strictly Internet Explorer. The viewing and management capabilities are much poorer than at the recorder itself.
The best option is to work from any browser plus using a special program. The ability to fully manage the registrar, the same as on it.
Between these polar variants, there are plenty more. As a rule, work through the browser is arranged like this: when you first access it, you are asked to install a plugin (often as an exe file).
7. Internet opportunities.
Most modern recorders support mobile devices on Android and iOS (iPhone, iPad). In order to view a live picture from a mobile device (and on some models, also watch recordings and manage the recorder), the recorder must be connected to the Internet with a real IP address. To work with real dynamic addresses, all registrars support multiple DDNS services.
Some registrars can work with USB-modems, but for their work it is necessary to connect the "real IP" service from the cellular operator.
8. Quality programs.
Unfortunately, recorders from different manufacturers have different protocols for remote viewing and management, so programs for PC and mobile devices are different for everyone. Convenience and quality of these programs may vary significantly.
For example, in one case, in order to see the image from the cameras on a mobile device, it is enough just to run the program (of course, provided that all settings, logins and passwords were saved in advance), and to switch cameras, it is enough to navigate the screen.
In the opposite case, you will have to perform a lot of inconvenient manipulations each time, and the cameras can even switch using additional menus.
9. Triplex, quadruplex, pentaplex ...
Often, sellers specify one of these words ending in “plex” as almost the main parameter of the registrar. This means that the recorder can simultaneously record, show recordings on a local monitor, work over the network and over the Internet. You should not pay attention to these "plexes". They all know how.
In this article I did not mention specific models and brands - the models change, but the principles of choice remain. My task is to send the choosing registrar to the right path.
In this article I will talk about the most common class - recorders working with analog video cameras. This recorder allows you to connect 4, 8 or 16 cameras, as well as 1 or more microphones. Recording is carried out on a hard disk that is installed inside the recorder. Most recorders are sold without hard drives. The disk is put usual computer with interface SATA. An analog monitor or TV, a VGA monitor can be connected to the recorder, some have an HDMI output. All modern recorders can connect to the local network and the Internet. It allows you to monitor, view records and manage the recorder from a computer and mobile devices.
Locally, the recorder is controlled by buttons on the front panel, an infrared remote control and a USB mouse.
')
Video inputs and recorder outputs - BNC connectors, audio inputs and outputs - RCA (tulips).
The signal from the camcorder is a regular PAL composite video signal. Security camera can be connected to the video input of a regular TV. Microphone inputs are linear 200 mV, so microphones must have a built-in amplifier.
The DVR can record in three modes: manually (by pressing the "record" button), by schedule, by motion detector. Many recorders can also record a few seconds before the start of the movement and a few seconds after it ends.
And now, actually, about the choice.
1. The number of inputs.
As I wrote at the beginning, recorders come with 4, 8, and 16 video inputs (very rarely with 9 and 32 inputs). The audio inputs are usually either the same as the video inputs or one or none. Four-channel recorders are considered budget, so they are much cheaper than the rest with the best parameters. An ideal 4-channel recorder will cost about 4,000 rubles, while an 8-channel recorder will be 11,000 rubles at best, and a 16-channel recorder will cost 22,000 rubles. What is the catch of cheaper multi-channel recorders will tell below. Of course, any recorder does not require connecting cameras to all inputs. You can use a 4-channel recorder with a single camera.
2. Resolution and recording speed.
These are the main parameters of any registrar. Ideally, the recorder should write each channel at a speed of 25 frames per second (Realtime) and full resolution of PAL 720x576 (D1). In video surveillance adopted the following notation for the image:
960H - 960x576
D1 - 720x576
4CIF - 704x576
HD1 - 720x288
2CIF - 704x288
CIF - 352x288
QCIF - 176x144
Very often, DVRs indicate the recording speed for all channels simultaneously. For example, if the technical parameters of a cheap 16-channel recorder indicate “Record - 100k / s (D1)”, this means that each channel will be written at a speed of 100/16 = 6.25 frames per second. At the same time, the same recorder can write 400 frames per second (25 fps per channel), but at a low resolution of CIF. Some cheap recorders allow non-linear redistribution of recording speed between channels. For example, with a total recording speed of 100 fps, you can write two channels at a speed of 25 fps, and the remaining fourteen at a speed of 3.5 fps.
This is the secret of the price of cheap registrars. They have a low write speed in full resolution. Until now, there are recorders that generally can not work at full D1 resolution and support only CIF, which is only 352x288 pixels. And I also met Chinese recorders, in which the two channels had a full resolution of D1, and the rest - CIF.
With 4-channel recorders, everything is simple and clear - you need to take Realtime D1 (100 fps on 4 channels), because there are a lot of them and they cost from 3000 rubles.
With 8- and 16-channel everything is more complicated. Realtime is twice as expensive as a D1 recorder at a speed of 5 or 6 fps. Do I need a Realtime Record? By and large, the information content of video surveillance does not affect, 5 frames per second is shown or 25. But 25 of course is more pleasant to watch. But registrars writing D1 at a speed of 6 fps cost from 5,000 rubles for an 8-channel channel and from 9,500 for a 16-channel channel.
But it’s definitely not worth saving on recording resolution and the registrar must support recording in D1 (720x576) or 4CIF (704x576) format.
The vast majority of modern recorders use the H264 codec, which allows to compress video strongly without significant loss of quality. A 500-gigabyte disk can be enough for several weeks to record 16 channels of motion detection.
3. Convenience record settings.
It is desirable that the recorder adjusts the brightness, contrast and chroma of the image for each channel.
It is important that the motion detector works well in the recorder, because the recording by the detector simplifies the subsequent search and significantly increases the storage time of the records on the hard disk.
Pay attention to the pre-recording and post-recording settings. It is convenient when the recorder records a couple of seconds before the start of the movement and after its termination, but when these values ​​cannot be set less than 5 seconds before the start and 10 seconds after the end of the movement, this greatly hinders: for each event, you have to watch the extra 15 seconds.
4. Ease of searching and viewing.
Different registrars search and view are organized differently. It is convenient when each event can be viewed separately, but after its display the recorder does not stop, but shows the next event.
5. Ability to save the record in a convenient format.
All recorders allow you to save video clips and frames to a USB flash drive. Many registrars are able to save data over the network on a computer.
I met registrars who saved the video in its format that is not compatible with anything. It was proposed to watch these files using a special player program, and it was impossible to convert them to generally accepted formats.
It is desirable that the recorder can save video files in AVI format.
6. Networking.
It is convenient when you can view a live picture, record and manage the recorder from a computer. All modern recorders have network capabilities, but for all this is implemented in different ways:
The worst option is to work only from the browser, and the browser is strictly Internet Explorer. The viewing and management capabilities are much poorer than at the recorder itself.
The best option is to work from any browser plus using a special program. The ability to fully manage the registrar, the same as on it.
Between these polar variants, there are plenty more. As a rule, work through the browser is arranged like this: when you first access it, you are asked to install a plugin (often as an exe file).
7. Internet opportunities.
Most modern recorders support mobile devices on Android and iOS (iPhone, iPad). In order to view a live picture from a mobile device (and on some models, also watch recordings and manage the recorder), the recorder must be connected to the Internet with a real IP address. To work with real dynamic addresses, all registrars support multiple DDNS services.
Some registrars can work with USB-modems, but for their work it is necessary to connect the "real IP" service from the cellular operator.
8. Quality programs.
Unfortunately, recorders from different manufacturers have different protocols for remote viewing and management, so programs for PC and mobile devices are different for everyone. Convenience and quality of these programs may vary significantly.
For example, in one case, in order to see the image from the cameras on a mobile device, it is enough just to run the program (of course, provided that all settings, logins and passwords were saved in advance), and to switch cameras, it is enough to navigate the screen.
In the opposite case, you will have to perform a lot of inconvenient manipulations each time, and the cameras can even switch using additional menus.
9. Triplex, quadruplex, pentaplex ...
Often, sellers specify one of these words ending in “plex” as almost the main parameter of the registrar. This means that the recorder can simultaneously record, show recordings on a local monitor, work over the network and over the Internet. You should not pay attention to these "plexes". They all know how.
In this article I did not mention specific models and brands - the models change, but the principles of choice remain. My task is to send the choosing registrar to the right path.
Source: https://habr.com/ru/post/170287/
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