[Vorbis-dev] Decoding for ambisonic Ogg audiob

[xiphmont at xiph.org]

On 2/26/07, Gregory Maxwell <gmaxwell at gmail.com> wrote:

> A) Simply output the B-format audio
> B) Produce a downmix
>   1) Mono.
>   2) Stereo  blumlein crossed pairs
>   3) Stereo UHJ
>   4) binaural
> C) Produce speaker feeds
>   1) Fully generalizable speaker feed decoder
>       (such as http://www.kokkinizita.net/linuxaudio/adec-pict.html)
>   2) G-format (fixed decode for the 5.1 layout)
>
> (A) is pretty much a no-brainer, and minus some polish on marking up
> the channel mapping we pretty much already do it today.

FWIW, vorbis 'Mapping 0' is what specifies the Dolby-style
multichannel output maps.  To say 'this doesn't support ambisonics
mappings' is only partially correct-- that's what I intended 'mapping
1' for.  There simply wasn't time to do any work on it before 1.0 as
the Vorbis project got discovered early and there was a push to
release the full 1.0 in a timely manner.

> I think that some form of downmix support will be an essential feature
> in the libraries. Most users will not have software or systems which
> are equipt to play b-format Vorbis files, at least initally. Anyone
> distributing such files will have a hard time if the files refuse to
> play at all for people.

There needs to be a distributed 'core' library for this, I agree.  It
shouldn't be part of libvorbis, but it would have to be part of the
distribution with libvorbis.

> A full speaker decoder as well as a binaural decoder will require a
> user-interface and can't really be done automagically. So I think they
> should be dropped from consideration as compatibility features for the
> core libraries.

I think the capability should be there, programmatically, even if a UI
for setting it up is not.

Monty