[Speex-dev] Mixing Codebook?

Ricardo Andere de Mello quilombodigital at gmail.com
Tue Mar 25 19:29:51 PDT 2008


maybe I´ll just answer "the number is 42". ;)

well... some guys did mixing using *G.722 *encoded frames... maybe we could
ask them: 8P

and a little off-topic, but fun for audio gurus like you, a very complicated
way to mix two mp3 streams:

[]s, gandhi

On Tue, Mar 25, 2008 at 10:01 PM, Jean-Marc Valin <
jean-marc.valin at usherbrooke.ca> wrote:

> > ok, lets get to the point. :)
> > I would need to mix some audio streams realtime. After googling a little
> > I had only two answers:
> > 1 - decode,mix,encode
> > 2 - lower quality, send streams at the same time and mix at the client.
> >
> > I didnt like either solutions.
> >
> > I´m not an audio expert, so I´m just saying something silly. I readed
> > that speex uses a fixed "codebook". So I think that in a simplistic way
> > this means that the encoded data are indexes in this codebook and some
> > transformation information.
> > Is it possible to create a "mixing codebook"? the idea is to generate
> > all the mix combinations of each entry in the codebook., so two encoded
> > frames could be merged and point to this different codebook, maybe
> > selected in the rtp header.
> Well, you *might* be able to do that at the frame level. Considering
> that 15 kbps corresponds to 300 bits. The the case of mixing two
> streams, you'd need a 600-bit codebook (2^600 entries). There's just a
> tiny implementation detail when it comes to storage. What you need to do
> to solve it is:
> 1) Find a way to encode a (very very) large number of terabytes in
> every electron (or other fundamental particle)
> 2) Manage to use every particle in the universe to store your codebook
> 3) Prevent the whole thing from turning into a black hole.
> You do what you want, but I suggest you go with one of the two solutions
> you listed above (decode,mix,encode or multiple streams).
>        Jean-Marc
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