[Vorbis-dev] Mapping = 1 Ambisonic Vorbis flag

[Oliver Oli]

Gregory Maxwell <gmaxwell <at> gmail.com> writes:

>> That's cos we might want more bits from yus guys later if / when we have
>> more than 16 channels ( more than 3rd order Ambi)
> 
> Hm?
> 
> Why would you want additional bits?
> 
> B-format support is going to need a channel map even for second order
> because you may want to do mixed order-representations.  A commons
> usage would be second-order horizontal only (this is what would
> probably be used for 5.1->b-format conversions), or things like
> third-order horizontal plus first order height (which is more of a fit
> for speaker arrays which can reasonably be constructed in a
> residential setting).  I wouldn't use the mapping to indicate H/V
> orders.
> 
> Or were you referring to the lack of a canonical selection of
> orthogonal harmonics for higher orders?  I thought that had been
> resolved. If not, I think it probably should be rather than expecting
> Vorbis to handle it.
> 


There where two proposals in the sursound mailing list. The first one was a
simple non-extensible static mapping (similar to the current type 0),
something like:

1:  W
2:  WX
3:  WXY
4:  WXYz
5:  WXYUV
6:  WXYzUV
7:  WXYUVPQ
8:  WXYzUVPQ
9:  WXYzUVstr
11: WXYzUVstrPQ
16: WXYzUVstrPQnolmk

The second proposal, was from Sampo Syreen, who suggested to add the full
OggPCM (option 2) channel mapping, which I think would be a very good idea,
because we would also add support for surround formats >5.1.

Both proposals support B-Format up to third order, full, horizontal-only or
mixed orders. But OggPCM should be extensible above 4th order I guess. 

I don't know how well this fits into the Vorbis (or Ogg) headers.