[vorbis] mixing and 'downgrading' of vorbis-files

[Beni Cherniavsky]

On Fri, 16 Feb 2001, Kristoff Bonne wrote:

> Greetings,
> 
> On Thu, 15 Feb 2001, Aaron Porter wrote:
> >> Concerning 'mixing' music, it would be interesting to be able to mix two
> >> ogg-files without the need to decode and re-encode the files?
> >> Also, can it be done to mix vorbis-file with different data-rates?
> 
> > It shouldn't be too hard to have two separate Vorbis streams that get mixed
> > by the player but I don't think there's any software that does that yet.
> Now, the idea would be to mix two vorbis-streams into a new vorbis-stream.
> 
> Consider a radio-station streaming in ogg; in which one song is faded out
> while the new one is already started or mixing a song with the voice of
> the radio-host. (considering his/her voice is encoded into ogg at real
> time).
> So, how can you avoid loss of quality by not having to decode and
> re-encode your signal.
> 
> I guess this is more a question concerning the ogg-codec. Is it possible
> in the mathymatical model of the codec? 
> 

This resembles a question I asked once (on the vorbis list, IIRC): can the
volume of a vorbis stream be changed without a decode-encode cycle?  My
idea then was to scale the vectors of the codebook - this is probably not
enough, as something needs to be done with the floor, if I undestand the
encoding correctly (Naagh... ;-).

I didn't get an answer then though, so could somebody answer now?

The only thing missing then for mixing in the vorbis domain is the ability
to sum two vorbis streams (which is probably the harder of the two :-).  
Anyway, it would be cool to do only volume scaling if addition is
impossible.


-- 
Beni Cherniavsky <cben at crosswinds.net>
                 (also scben at t2,cben at tx in Technion)

  (/bin/ch x)^2 == (/bin/sh x)^2 + 1

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