Bit rate is basically the ratio of the number of bits conveyed or processed repeatedly per unit of time. Bit rate is commonly quantified in bits per second (bps), kilobits per second (Kbps), or megabits per second (Mbps).
Bit rate is also used to describe the quality of a video or an audio file. You can see bit rate when downloading music or video files on an internet. An audio file at 192 Kbps will sound better and clearer than the same audio file at 160 Kbps. This is because the number of bits per second to represent audio data is higher. Generally, a video file at 9Mbps will look better than the same video file at 3Mbps. The quality of a video or an audio file can vary greatly at different bitrates.
The different bitrates for the same files are achieved through a process called compression. It is used to offer content at different quality levels because Internet access speeds vary greatly depending on device, carrier and location. For example someone viewing a video from a laptop connected to a broadband service supporting download speeds of 20 Mbps can easily stream an HD movie but the same person streaming the HD movie over a mobile network may need to watch in SD quality. (See compression for more information on how the type of compression can affect quality).
Bit rate is also important for calculating the cost of streaming services. Higher bit rates result in higher overall bandwidth usage and ultimately a higher cost. The ideal situation for streaming is to offer the best bit rate your viewers can use while still remaining in budget.