[CELT-dev] Surround Sound

[Gregory Maxwell]

On Tue, Dec 28, 2010 at 2:14 AM, Kip Warner <kip at thevertigo.com> wrote:
> Hey folks,
>
> As I understand it, the vorbis codec had support for a channel count >
> 2, but that it didn't explicitly state the channel binding for channels
> 3, 4, ... . I'm assuming that with enough fiddling, it would
> theoretically be possible to use a 5.1 stream encoded into vorbis.

The vorbis codec has always had well specified bindings for 5.1
surround (6.1/7.1 were added more recently).

The libvorbis encoder didn't do coupled encoding of >2ch, so 5.1 took
more bitrate than it could have, but coupling was added to the
libvorbis encoder last year.

Monty documented the process of adding coupling in a number of posts
at http://people.xiph.org/~xiphmont/demo/ (under surround
optimization). The pages also include a number of demo surround vorbis
files.

> From what I know of the CELT codec, it handles either only mono or
> stereo. Is that correct?

Correct.

In our (now defunct) RTP draft we specified a signaling and mapping
scheme to setup surround using mono/stereo CELT instances[1].  It's
been my intention to update our Ogg mapping for CELT to support the
same, but I'm currently waiting on seeing how multichannel is signaled
with Opus.





[1] http://tools.ietf.org/html/draft-valin-celt-rtp-profile-01