What Is a Constant Bit Rate?

Constant bit rate is a term used to describe the quality of service (QoS) of a communication, which means that the file is a bit rate from beginning to end. Compared to VBR and ABR, the compressed file is very large, and the sound quality will not be significantly improved compared to VBR and ABR.

Constant

Regardless of whether it is audio or video encoding, CBR encoding has the advantages of fast compression and can be supported by most software and equipment; and CBR is very useful when performing multimedia communication in a bandwidth-limited channel. Because the highest bit rate is limited at this time, CBR can better use such channels. However, CBR is not suitable for storage, because CBR will not have enough code rate to encode complex content parts (thus causing quality degradation), and at the same time, some code rates will be wasted. When using CBR encoding, the bit rate and size of the encoded stream are known before encoding. For example, if you encode a three-minute song at 32,000 bits per second, you know that the file size is approximately 704 kilobytes (32,000 bps x 180 seconds / 8 bits / byte / 1,024). ^[2]

The output of most coding schemes are variable-length codewords, such as Huffman coding or run-length coding, which makes it difficult for the encoder to achieve perfect CBR. The encoder can partially solve this problem by adjusting the quantization (thus adjusting the encoding quality). If the padding code is used at the same time, the CBR can be perfectly achieved. (Sometimes, CBR also refers to a very simple encoding scheme, such as sampling a 16-bit precision audio data stream to obtain an 8-bit precision data stream.)