[vorbis] Re: [vorbis-dev] intro to compressed audio tutorial

[volsung at asu.edu]

On Thu, 7 Feb 2002, Beni Cherniavksy wrote:

> one onf several adjustant frames (or something like this).  So the term
> CBR is almost always incorrectly used to describe ABR which is the right
> term.  The vorbis position is to always say "ABR".  RC3 managed mode uses
> a 2 second window IIRC.

<p>Some would argue that CBR really is just a special case of ABR where the
window size is the same size as the smallest block of audio.  Given that the
smallest block of audio in vorbis is either 256 or 2048 samples, "CBR" would
be incredibly constraining.  I would imagine nearly all audio playback systems
that have limited bandwidth have big enough buffers (to compensate for network
congestion) to handle an averaging window of 2 seconds.

[This is mostly directed at the document author rather than you, actually.]

The current vorbis encoder is quite flexible because it allows you to create
streams with an ABR target (average bitrate fixed), an ABR minimum (can't go
below a certain bitrate) or an ABR maximum (bitrate cap).  Monty has said that
in the next release, you will be able to make streams with ABR and VBR
properties.  Example: A quality 0 stream with a bitrate cap of 75 kbps.

Basically, vorbis is a VBR codec, but the encoder can enforce some ABR
properties if it so chooses.


---
Stan Seibert

<p>--- >8 ----
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