[Vorbis-dev] Mapping = 1 Ambisonic Vorbis flag

[Martin Leese]

Sampo Syreeni <decoy at iki.fi> wrote:
...
> Third, Richard Lee's argument about ambisonic channel metadata carries
> over to channel semantics in general: you need to know what each channel
> means from the word go, so channel mappings need to be present in the
> codec initialisation headers, and not, say, in Skeleton. Otherwise we're
> going to experience delay before the channels can be played properly,
> which isn't going to be appreciated by the better part of people who are
> used to fast synch in DVDs, big screen movies, and indeed the other
> container formats.

No, the Skeleton stream comes ahead of all
other streams.  (In Ogg-speak this is "chaining".)
Note also that the intention is that *every* Ogg
file should include a Skeleton stream.  (The
problem, as you might expect, is backwards
compatibility.)

> So, while I *do* undertand (and perhaps even support) the idea that the
> ambisonic mapping in Vorbis should be as simple as possible, I *still*
> think the above reasoning for it is gravely mistaken.

Well, the simplest mapping is to let Channel
Mapping = 1 signify a B-Format Vorbis stream.
That's all you need for third-order.  You don't
even *need* a Skeleton stream (although it
would be useful to make one mandatory in
Ogg files containing a Vorbis B-Format stream).
Fourth-order and higher needs more metadata
but, as the Skeleton stream is intended for
metadata about other streams, that's a good
place for it.

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