[Vorbis-dev] Mapping = 1 Ambisonic Vorbis flag

[Oliver Oli]

On Wed, Sep 10, 2008 at 1:20 AM, Richard Lee <ricardo at justnet.com.au> wrote:
> As it so happens, mixed orders up to 3rd are implicitly specified by the number of channels.
>
> This is described Martin Leese's "File Format for B-Format" page at http://www.ambisonia.com/Members/mleese
>
> There is no need for a channel map for the forseable future.

Are you sure? :-)

> When we start distributing 4th order stuff (which requires >16 speakers) we can get around this by having missing channels simply silent.  Vorbis compression is very efficient at coding silence.  Thanks to Gregory Maxwell for this excellent suggestion on the sursound forum.

Fons killed that proposal already on the sursound list. The Ambisonics
decoder have to be setup before the playback starts. A silent channel
is still a channel that at any point in time could become non-silent.

>> The second proposal, was from Sampo Syreen, who suggested to add the full OggPCM (option 2) channel mapping, ...  because we would also add support for surround formats >5.1.
>
> This can stay in Ogg.  It is a VERY bad idea to have with Vorbis Ambi (Mapping = 1)  They are fundamentally VERY different in their approach.

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.

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.