Keywords: CCTV, Security Camera, IP Camera, DVR, NVR, Bit Rate, Constant Bit Rate, Variable Bit Rate
First of all, let’s start with the word, bit. A bit is an acronym for “binary digit,” the smallest possible unit of information in digital computing and networking. 8 bits make one byte. 1024 bytes make 1MB. 1024MB make 1GB, 1024GB make 1TB. You should probably be familiar with the TB now, because all our CCTV, and IP camera solutions are based on multiple TB harddisk capacity.
Coming back to bit rate, bit rate is the number of bits that pass a given point in a telecommunication network in a given amount of time, usually a second. A bit rate is usually measured in some multiple of bits per second – for example, kilobits, or thousands of bits per second (Kbps). So when we talk about the bit rate for a CCTV camera, or IP Camera, it can refer to the number of bits transferred per second for the combination of video and audio streams, again, usually in Kbps.
Constant bit rate (CBR) and variable bit rate (VBR) are the main types of bit rate encoding.
Constant Bit Rate
With constant bit rate, a fixed bit rate and bandwidth is used throughout the entire track or encoded video file. This is favoured when only limited bandwidth is available, because bit rate that can be predefined. In addition, with CBR, the file size is more predictable. However, the disadvantage with CBR is that when there is, for instance, increased activity in front of the CCTV camera that results in a bit rate that is higher than the target rate, the restriction to keep the bit rate constant results in a poorer image quality and lower frame rate.
Variable Bit Rate
With variable bit rate, a changeable bit rate (hence the bandwidth) is used throughout the encoded CCTV or IP Camera video file. The variability of bit rates allows for video to be recorded at a lower bit rate when the video scene on screen is less complex, and at a higher bit rate when the video scene is more complex. This eventually means that bandwidth use will increase when there is a lot of activity in a scene and will decrease when there is no motion. This is often desirable in CCTV surveillance applications where there is a need for high quality, particularly if there is motion in a scene. In short, image quality is better with variable bit rates than with constant bit rates. However, the disadvantage is that pre-planning the CCTV and IP camera video storage requirements becomes more challenging as the bit rate changes with the complexity of scenes.
All our CCTV products, including NVRs, DVRs, Analog CCTV camera, and IP cameras will allow you to choose either constant or variable bit rates when recording video.