VBR

VBR, or variable bit rate, is a method of encoding in which the number of bits used to represent each unit of time varies according to the complexity of the data. It is commonly used in audio and video codecs, as an alternative to constant bit rate (CBR) and average bitrate (ABR).

In audio, VBR analyzes short blocks of audio and allocates more bits to complex passages (where the signal changes rapidly) and fewer bits to simpler passages, guided by perceptual models of hearing. The result is typically higher perceived quality for the same average file size, or smaller files for a given quality. VBR can be implemented with a target quality level (constant quality) or with an average bitrate target.

In video, VBR adjusts the bitrate depending on scene complexity, detail, motion, and other factors. This can improve efficiency, delivering higher quality during complex scenes and lowering bitrates during simpler ones. However, VBR can complicate streaming, seek operations, and buffering, and some playback devices or protocols expect or optimize for CBR.

Common formats that support VBR include MP3 and Ogg Vorbis for audio, and various modern video codecs with bitrate-optimization features. Containers like MP4 and MKV often store VBR streams. In practice, VBR settings are typically chosen to balance quality targets with compatibility and streaming requirements.

VBR remains widely used for storage and distribution of music and video where storage efficiency and quality are prioritized, but in live streaming and certain broadcast contexts CBR or ABR may be preferred for predictability.