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On the Definition of Video Rate

Oct 03, 2017

solar 3G/4G security camera

Video bit rate


Video bit rate is the data transmission unit time to send the number of data bits, we generally use the unit is kbps thousand per second.


The higher the sampling rate, the higher the accuracy of the unit, the higher the accuracy, the closer the processed file is to the original file, but the file size is proportional to the sample rate, so that almost all of the Coding format is how to use the lowest bit rate to achieve the least distortion, around the core derived from the cbr (fixed bit rate) and vbr (variable rate), are in this regard to do the article, but the total Is not absolute, for example, for an audio, the higher the bit rate, the smaller the proportion of compression, the smaller the loss of sound quality, sound quality and sound closer.


Calculation formula


The basic algorithm is: [code rate] (kbps) = [file size] x8 x 1024 / [time] (seconds).


Bit rate principle:


1, bit rate and quality is proportional, but the file size is also proportional to the bit rate. This is to keep in mind.


2, bit rate exceeds a certain value, the quality of the image does not have much impact.


3, DVD capacity is limited, whether it is the standard 4.3G, or ultra-engraved, or D9, have the limit. The information in the video bit rate computer is represented by binary 0 and 1, where each of the 0s or 1s is called a bit, expressed in lowercase b, bit (bit); capitalized B means byte, byte, one Byte = eight bits, ie 1B = 8b; the previous uppercase K means 1024 means 1024 bits (Kb) or 1024 bytes (KB). Indicates the size of the file, usually using bytes (KB) to represent the size of the file.


Kbps: First of all to understand is that ps refers to / s, that is, every second. Kbps refers to the speed of the network, that is, how many thousand bits per second of information (K said thousands of bits, Kb said that the number of thousands of bits), in order to appear intuitively on the network transmission speed, the general companies are Use kb (thousands) to represent. 1KB / S = 8Kbps. ADSL Internet access speed is 512Kbps, if converted to bytes, that is 512/8 = 64KB / S (that is, 64 kilobytes per second).


4, in general, if it is 1M broadband, on the Internet can only see more than 1024kbps video, more than 1024kbps video can only wait for video buffer to smooth viewing.


Classification of Rate in Video Surveillance


Fixed bit rate


(English: Constant bitrate, referred to as CBR), is the static (constant) bit rate means, CBR is a fixed sampling rate compression. For video coding, CBR coding refers to the amount of data (or the input bit rate of the decoder) of the encoder per second. It should be a fixed system (constant). The encoder detects the complexity of each frame image and then calculates the bit rate. If the bit rate is too small, fill the useless data to make it consistent with the specified bit rate; if the code rate is too large, it is appropriate to reduce the bit rate, but also to the same code rate consistent. Therefore, the fixed bit rate mode coding efficiency is relatively low. In the fast moving picture part, the picture details are more, generally need more bits to describe, but because of forced to reduce the bit rate, it will lose some of the details of the screen information, and the screen blurred, unclear phenomenon. For audio compression, such as MP3, bit rate is the most important factor, it is used to indicate how many bits per second of audio data, the higher the value, the better sound quality. CBR uses fixed bit rate encoding audio, a MP3 from beginning to end for a fixed value, such as 128 kbps encoding. Simply put, is to ensure smooth bit rate fluctuations, but can not guarantee the image quality and sound.


Variable rate


(English: Variable Bit Rate, referred to as VBR), VBR can change with the complexity of the image, so its coding efficiency is relatively high, fast motion picture mosaic is very small. Encoding software in the compression, according to the video data, instantly determine what bit rate, so that both to ensure the quality, but also take into account the file size. In this way, the encoding program can choose from a variety of video quality from the worst audio and video quality (typically the highest compression ratio at this time) to the best audio and video quality (typically the lowest compression ratio at this time). When the video file is encoded, the encoding program tries to keep the quality of the selected file, and selects different bit rates for different parts of the video file. For example, the use of MP3 format audio codec, audio files can be 8 ~ 320kbps variable rate of compression, get a relatively small file to save storage space. It means that the codec can automatically adjust the bandwidth according to the size of the data volume, and the bandwidth is larger when the image changes faster and the color is rich; the image changes slowly and the bandwidth is less abundant when the bandwidth is smaller To ensure the quality of image recording while maximizing network bandwidth savings.

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