[MPlayer-users] Re: Mplayer/ogm/ogg

[Jason Smith]

On Wednesday 18 December 2002 10:17 am, gabor wrote:
> i'm just curious....
>
> what's the advantage of having 6channel-vorbis instead of ac3?
>
> smaller size for same quality?
>
> and that 6channel-vorbis: it's encoded as 3 stereo channels, or does it
> encode intelligently? something like encode the basic info + the 6
> differences?

(I'm using Gentoo, so YMMV)

Check out /usr/share/doc/libvorbis-1.0-r1/txt/doc/stereo.html

I'll paste a sample to whet your appetite:

Abstract

 The Vorbis audio CODEC provides a channel coupling mechanisms designed to 
reduce effective bitrate by both eliminating interchannel redundancy and 
eliminating stereo image information labeled inaudible or undesirable 
according to spatial psychoacoustic models. This document describes both the 
mechanical coupling mechanisms available within the Vorbis specification, as 
well as the specific stereo coupling models used by the reference libvorbis 
codec provided by xiph.org. 

Mechanisms

[snip]
These two general mechanisms are particularly well suited to coupling due to 
the structure of Vorbis encoding, as we'll explore below, and using both we 
can implement both totally lossless stereo image coupling [bit-for-bit 
decode-identical to uncoupled modes], as well as various lossy models that 
seek to eliminate inaudible or unimportant aspects of the stereo image in 
order to enhance bitrate. The exact coupling implementation is generalized to 
allow the encoder a great deal of flexibility in implementation of a stereo 
or surround model without requiring any significant complexity increase over 
the combinatorially simpler mid/side joint stereo of mp3 and other current 
audio codecs.

 A particular Vorbis bitstream may apply channel coupling directly to more 
than a pair of channels; polar mapping is hierarchical such that polar 
coupling may be extrapolated to an arbitrary number of channels and is not 
restricted to only stereo, quadraphonics, ambisonics or 5.1 surround. 
However, the scope of this document restricts itself to the stereo coupling 
case.

HTH.  AFAIK, vorbis is well-suited for 5.1 and more.

-- 
Jason Smith