Short comments (to text below):
(1)
The ambisonics input channels can’t be coded in some 7.1 (channel
coupling, LFE) style, agreed.
With opus you seem to need channel mapping #255, not #1 - the latter
corresponds to (classical) 2D surround sound layouts.
(2) I believe that FB is already using up to 11 channels coded with
opus, although I am not absolutely sure about. (Could say more about
this in a few weeks, hopefully.)
(3) Multi-channel != (classical) 5.1/7.1 surround sound. In fact
surround sound is not a synonym for 5.1/7.1.
We are on the surround list, so should know about this!
But now we are getting slightly confused: Xipg.org’s Opus or Flac
don’t have to care about Dolby Digital or DD+ 5.1/7.1, right? So maybe
you mean 5.1/7.1 channel mapping?
To claim that 5.1 is “Dolby” doesn’t make sense. (There is an official
ITU layout standard, and many versions implemented/defined by DTS,
Mpeg, Sony and “anybody else”.)
https://www.itu.int/dms_pubrec/itu-r/rec/bs/R-REC-BS.775-3-201208-I!!PDF-E.pdf
So (righteously) you can implement 5.1 and 7.1 audio tracks since Vorbis...
(4) A lossless compression format could be used for mastering. I meant this.
Best,
Stefan
- - - - - - -
Citando Marc Lavallée <m...@hacklava.net>:
Le 2018-07-29 à 05:56 PM, Stefan Schreiber a écrit :
1. I believe that the opus encoders/decoders have always supported
more than 8 channels.
Correct, but when encoding 8 or less channels, correlation is
applied in ways that are incompatible with Ambisonics; for example,
the LFE channel is filtered... With more than 8 channels, Opus don't
correlate channels, but it does now if the input stream is
Ambisonics (and if the Ambisonics mode, disabled by default, is
compiled in).
2. The next question is what ogg channel mapping and consequently
real-world browsers allow...
But in some sense the hack you did is known. (More complicated is
maybe to make it work...)
I tried only with 4 channels. It worked. I don't know if browsers
are now capable to support more than 8 channels. If the Octomic is
getting popular with VR content producers, maybe browsers will start
supporting streams with more than 8 channels (without systematically
down-mixing them to stereo).
3. If they already plan to issue some ogg ambisonics standard
(using ogg opus of course) since at least 2016: You also need an
associated mastering standard, which would not change or compress
any audio data. Correct?
So what is “political” about extending the channel count of FLAC?
Multi-channel still mean Dolby 5.1 or 7.1. There's an inertia
because "standards" were designed as vendor lock-ins.
Compromise proposal:
4. So let’s maybe use .wav or .caf for the “mastering format”.
Microsoft and Apple already allow more than 8 channels... 🤔
Sure. Lossy codecs are not suited for mastering.
P.S.: “Joint stereo” you could classify as parametric coding.
Ok.
Marc
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