[Vorbis-dev] e: Mapping = 1 Ambisonic Vorbis flag

[Martin Leese]

"Oliver Oli" <oliver.oli+0815 at gmail.com> wrote:

> Are we sure we know what we are talking about? What is Ogg, what is
> Vorbis and what OggPCM? Maybe one of the developers can bring
> enlightenment to us :-). As I understood it OggPCM is equivalent to
> Vorbis. So it's not Ogg/PCM, but Ogg/OggPCM. Please correct me if I'm
> telling utterly crap.

Yep, that's it, the OggPCM stream goes into
an Ogg container.  (Note that, unlike Vorbis,
OggPCM is uncompressed PCM, but you were
obviously speaking at the conceptual level.)

> I don't see any reason why a flexible universal channel mapping
> approach is a VERY bad idea. Just don't call it Ambisonics channel
> mapping. There are hybrid formats, how could you describe these with a
> simplistic Ambisonics-only channel mapping? I'm thinking of B+ Format
> (Ambisonics + Stereo) or maybe WXY(Z) plus a center channel and
> optional LFE as a 5.1 alternative.

It depends on what your goal is.  If you what to
accommodate hybrid formats, as OggPCM can
do, then things become complicated.

If you want a format just for B-Format then life
is very much simpler.  Up to third order the
only metadata you need is the channel
mapping type = 1.  All other information can
come from the number of channels.

For fourth-order and higher you need
additional metadata, specifically two integer
numbers for the horizontal- and height-order.
The last time this was discussed, the Xiph
crowd suggested these could go as Key-Value
pairs in the message header fields in the Ogg
Skeleton stream.

Regards,
Martin
-- 
Martin J Leese
E-mail: martin.leese stanfordalumni.org
Web: http://members.tripod.com/martin_leese/