TopTechnical DictionaryBit rate

Bit rate

Bit rate (bit rate) is the amount of data stored or transmitted via a transmission channel per second. For IC cameras or recorders, the bit rate is measured in megabits per second (Mb/s) and the higher the bit rate (bits stored or transmitted in 1 second), the higher the video quality.

 

Bit rate is often mistaken for the bandwidth, since both values are expressed using the same unit. However, the bandwidth defines the transmission capacity of a communication channel, while the bit rate defines an instantaneous data stream volume.

 

The bit rate can be calculated from the following formula:

 

K = V log2(n)

 

Note:
V – character generation rate in bods (changes in transmission medium per second)
n – signal value (binary = 2)

 

In IP cameras, in particular offering 1920x1080 px (Full HD) or higher resolution, the video quality may differ between the models depending on the maximum bit rate (bit rate). Even if both cameras use the same compression method (e.g. H.264), the video quality will be significantly higher in a model with a higher maximum bitrate, however, it will require higher bandwidths and more storage space.

 

Bit rate can be constant (CBR – Constant Bit Rate) or variable (VBR – Variable Bit Rate) depending on the technique used for data transmission.

 

Constant bit rate means using the same number of bits in a data stream during data transmission or storage, regardless of the actual video or image quality. It can be useful at limited bandwidths, e.g. media streaming during multimedia transmission via the internet, however it is not suitable for saving multimedia data, where the CBR may include redundant information, e.g. for non-complex video sequences with low variability in time and may be insufficient for very dynamic video sequences (loss of quality).

 

Variable bitrate means that the number of bits varies per unit of time. The purpose of this method in IP cameras is to maintain a constant output image quality regardless of the input data (e.g. image dynamics, colour and contrast differences) and not a constant number of bits per unit of time. The technique can also be used for storing multimedia data on mass storage devices providing more optimum usage of the available disk space.

 


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