[vorbis] Ogg/Vorbis Downsampling?

[craig duncan]

Gregory Maxwell wrote:
> 
> On Wed, Mar 21, 2001 at 09:50:34AM -0500, craig duncan wrote:
> > I've read this a number of times and it finally occurred to me to ask for
> > clarification.  I think i understand "no tools yet" as far as the server doing
> > the streaming goes but does a vorbis encoded stream (lack of tools aside)
> > currently implement this concept so that, were the tool available, the stream
> > could be peeled down to a lower bit rate?  I'm guessing the answer is yes, but
> > "format is designed to be able to do this" sounds a little ambivalent on the
> > matter.  Is this because it _should_ work but simply hasn't been tested yet?
> 
> Yes, you could do it with the files you produce today. But, the results
> would be sub-optimal because the encoder doesn't expect you to be doing such
> a thing. In the future the encoder will produce output which is a bit
> differnt (cascaded codebooks) so it can express to the bitrate peeling
> utility what information it can throw away first.

Ah, thanks.  Do you mean to say that (currently), as you move closer to the
end of each packet, the data in no way "correlates" with just the info
associated with higher bit rates?  (So you _could_ peel it now, but the result
would be random in terms of what was saved and what was thrown away?)  It
wouldn't be accurate to describe this as "sub-optimal", though. :)  "express
to the bitrate peeling utility what info it can throw away first" seems to
imply that the "algorithm" isn't as i understood it, e.g. throw away however
much you want starting from the end of the packet.  Maybe you couldn't throw
away an arbitrary amount but, rather, the amount that corresponded to what was
encoded in a pass across the frequency spectrum, which is a minor wrinkle.  Is
that what you mean, or is my idea about this misguided?

craig

craig

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