#video recorder
Digital video recorders.
What to look for when choosing a recorder?
Video recorder recording quality:
The recording quality of a video recorder is determined by two parameters — resolution and recording speed. Recording quality is one of the main criteria when choosing a digital video recorder.
To correctly assess the quality of the resulting video image, it is necessary to find out at what recording speed the required resolution is provided for each channel, for example: 704×288 px at 25 fps or 704×576 px at 12.5 fps.
Recording resolution is the number of dots (pixels) that make up the video image: 352×288, 704×288, 704×576, etc.
Recording speed is the total number of frames recorded per second for all video channels.
Example: for a 4-channel video recorder, the recording speed is specified as 100 fps, i.e. each channel can record at a speed of 25 fps. (100?4). For the PAL standard, the maximum recording speed per channel is 25 fps — real-time recording.
Video compression format when recording to a hard drive:
When choosing a video recorder, you need to pay attention to the video compression format used in it. MPEG4 and H.264 (the most relevant today) are commonly used.
MPEG4 is a format designed to compress the flow of audio and video information. These video recorders have an outdated element base.
H.264 – this format uses the latest algorithms for compressing audio and video information and is a continuation of the development of the MPEG4 format.
Distinctive features of this standard are improved color rendition and increased image clarity. Video information recorded in the H.264 format takes up approximately 2 times less space on the hard drive than recording in the MPEG4 format.
Video recorder disk space:
Video information coming from all CCTV cameras is saved to the hard drive of the recorder. How can you determine the required volume of hard drives based on the time interval you need to record during?
To determine the required disk space, you need to operate with several components:
- know the resolution at which you need to record (352×288 — 704×576 px).
- know the speed at which you need to record (12.5 — 25 fps).
- frame size (3 — 15 KB, the advantage of the H.264 compression format).
- desired number of simultaneously recorded video channels (1 — 16).
The size of the video recorder archive is determined by the following parameters:
- the number of hard drives that can be installed in the video recorder.
- the ability to connect an external disk drive, including a Raid array — the video compression format.
Also, modern digital video recorders provide the ability to archive the necessary video data using backup functions on: CD and DVD disks, removable hard drives or Raid array, USB flash drives and over the network.
Video outputs of the video recorder:
To view video information on an analog monitor, the video recorder has a composite BNC video output, but if you plan to view it on a digital monitor, you will need a VGA (D-SUB) video output.
The presence of a BNC output allows you to connect an analog monitor over a significant distance (up to 3 kilometers, using special equipment).
Some video recorders have end-to-end video outputs, with which you can transmit a signal from each video surveillance camera separately to other recording or display devices.
Many video recorders have an alarm video output — for instant display of images on the monitor from video surveillance cameras in the event of an alarm event (motion detection, etc.).
Video recorder audio inputs:
Modern models of video recorders have from 1 to 16 RCA audio inputs. When designing a video surveillance system, you need to choose a model with the number of audio inputs you need.
Video recorder network functions (TCP/IP):
Video recorders with a network function provide the ability to connect to them any personal computer in an existing network for remote viewing of video images and recording.
Some video recorders provide the ability to configure their parameters over the network, which significantly speeds up and reduces the cost of servicing the video surveillance system.
There are video recorders that have a two-way audio channel over the network. This means that you can not only listen to and record audio information, but also transmit it — make announcements or transmit commands.
A very useful function of video recorders is the transmission of information over the network to email, and in some cases to an FTP server, messages about any events: motion detector activation, hard drive failure, alarm input activation, loss of signal from a camera, etc.
Control of external devices via a video recorder:
- Video recorders have many functions for controlling external devices.
- PTZ control of PTZ surveillance cameras via the RS-485 interface.
- control of PTZ cameras by alarm.
- when alarm inputs, motion detectors are triggered, or video signal is lost on any channel.
- the video camera rotates to the specified position.
- control of alarm outputs. Depending on the capabilities of specific models, you can configure the alarm to be generated when signals are received from alarm input sensors, motion or sound detectors are triggered, or when a hard drive is faulty, or when a signal from any camera is lost.
- control of other video recorders: several “slave” video recorders are connected to the “master” video recorder via the network, while it is possible to control, remotely monitor and view the archive from the “slave” video recorders.
Availability of software for the central video surveillance post:
This parameter is important for video surveillance systems with a large number of video surveillance cameras (more than 16). Below are the capabilities of such software:
- simultaneous viewing of images from all DVRs connected to a network on several monitors.
- remote control of DVR settings.
- viewing video recordings from individually selected DVRs.
- creating maps of surveillance objects, and much more.
Intelligent functions of digital DVRs:
Modern DVRs, in addition to the standard set, are equipped with additional intelligent functions.
Such capabilities are usually associated with the analysis of video recording or «live» image, and the issuance of appropriate signals or messages:
- search for a recording by motion detector in a specified area of the frame.
- detector of «abandoned objects».
- face recognition.
- recognition of car numbers.
- determining panic by changing the trajectory of people's movement.
- searching for a record by a cash transaction.