There's a IETF proposal from folks at Google for "Ambisonics in an Ogg Opus Container", based on
Nachbar, et al., Ambix - A Suggested Ambisonics Format. 3rd International Symposium on Ambisonics and Spherical Acoustics, Lexington, KY (2011) and the idea of a default stereo decode from Etienne Deleflie's Universal Ambisonic work https://tools.ietf.org/html/draft-ietf-codec-ambisonics-07 Martin Leese has posted pointers to it here from time to time. Early versions had errors, which I informed them of and were fixed in later versions. Aaron Heller (hel...@ai.sri.com) Menlo Park, CA On Sun, Jul 29, 2018 at 4:45 PM, Stefan Schreiber <st...@mail.telepac.pt> wrote: > > 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 -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://mail.music.vt.edu/mailman/private/sursound/attachments/20180729/c6f73626/attachment.html> _______________________________________________ Sursound mailing list Sursound@music.vt.edu https://mail.music.vt.edu/mailman/listinfo/sursound - unsubscribe here, edit account or options, view archives and so on.
