Variable bitrate

Encyclopedia : V : VA : VAR : Variable bitrate

Variable bitrate (VBR), or less commonly variable bit rate, is a term used in telecommunications and computing that relates to sound or video encoding. As opposed to constant bitrate (CBR), VBR files vary the amount of output data per time segment. VBR allows a higher bitrate (and therefore more storage space) to be allocated to the more complex segments of sound files while less space is allocated to less complex segments. The average of these rates is calculated to produce an average bitrate for the file that will represent its overall sound quality.

MP3, WMA, Vorbis, and AAC files can optionally be encoded in VBR.

Pros and cons

The basic argument for using VBR streams is quite simple and compelling - it produces a better quality-to-space ratio compared to an equivalent CBR algorithm.

However, there are some disadvantages:

Encoders and decoders are typically more complex
Possibly due to the above, VBR support is not as ubiquitous as CBR. For instance, many commodity set top box players support CBR but not VBR playback of mp3 files.
mp3 Files encoded with VBR may not play on VCD/DVD players. It usually shows an error "MP3 FILE UNPLAYABLE"

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