|
What is VBR?
VBR stands for Variable Bit Rate. The bit rate of a coded audio file is the number of bits (binary digits - 0s or 1s - bits of digital information) that are required to store 1 second of audio. An mp3 at 128kbps requires 128,000 (ish!) bits to store 1 second of audio. The point of psychoacoustic coding is that you only store the audible part, but just how much information is needed to represent the audible part varies from 1 moment to the next. Silence doesn't contain very much information at all - rather than storing thousands of zeros, you could just store a code meaning "so many seconds of silence".
A Variable bitrate coder will vary the bit rate, depending on how much information is needed to store the audible part of a signal from moment to moment. If a decoder expects the same number of bits every second, this can really confuse it!
VBR is a new thing - why criticise decoders that haven't caught up yet?
A valid mp3 decoder must handle variable bitrate files. This was specified in the original standards document in 1993. For MPEG-1 or -2 layer 2, variable bitrate decoding is optional - for layer 3, it is mandatory.
___________________
Never again.
|
