In telecommunications and computing, bitrate is the number of bits that are conveyed or processed per unit of time. A bit is the basic unit of information in computing and digital communications. A bit can have only one of two values and may therefore be physically implemented with a two-state device. These values are most commonly represented as 0 and 1. The term bit is a portmanteau of the words binary digit. Simply put, the bitrate is the speed at which digital information (text, image, video, audio or metadata such as subtitles and closed captioning) can be transferred across a particular communication link.
In digital communication systems, the physical layer gross bitrate, raw bitrate, data signaling rate, gross data transfer rate or uncoded transmission rate is the total number of physically transferred bits per second over a communication link, including useful data as well as protocol overhead.
In digital multimedia, bitrate often refers to the number of bits used per unit of playback time to represent a continuous medium such as audio or video after source coding (data compression). The encoding bit rate of a multimedia file is the size of a multimedia file in bytes divided by the playback time of the recording (in seconds), multiplied by eight.
For realtime streaming multimedia, the encoding bit rate is the goodput that is required to avoid interrupt: In the case of file transfer, goodput corresponds to the achieved file transfer rate. The term average bitrate is used in case of variable bitrate multimedia source coding schemes. In this context, the peak bitrate is the maximum number of bits required for any short-term block of compressed data.
In digital multimedia, bitrate represents the amount of information, or detail, that is stored per unit of time of a recording. The bitrate depends on several factors, including whether the original material is sampled at different frequencies, uses different numbers of bits, is encoded by different schemes, or may be digitally compressed by different algorithms. Generally, choices are made between these in order to achieve the desired trade-off between minimizing the bitrate and maximizing the quality of the material when it is played.
If lossy data compression is used on audio or visual data (such as when transferring data for reference purposes, archiving and transcription), differences from the original signal will be introduced; if the compression is substantial, or lossy data is decompressed and recompressed, this may become noticeable in the form of compression artifacts. Whether these affect the perceived quality, and if so how much, depends on the compression scheme, encoder power, the characteristics of the input data, the listener’s perceptions, the listener’s familiarity with artifacts, and the listening or viewing environment.