[vorbis] bit rate

Vincent vincent.tiberghien at fsatie.ac.za
Tue Sep 23 04:19:08 PDT 2003



i have a hard time understanding clearly the different steps in the encoding
process, could someone tell me what are they and give a few lines to explain
each of these different steps.

According to me, it's the following :

meking different frames of the signal.
choose the mode to encode the different frame (huffman?).
encode the frame.
bitpacking
creation of the codebook.
writing the headers.
embending into ogg.

i think i forget a lot of things and i am probably also wrong.

<p>----- Original Message -----
From: "Karthik M" <karthik at siptech.co.in>
To: <vorbis at xiph.org>
Sent: Tuesday, September 23, 2003 8:52 AM
Subject: Re: [vorbis] bit rate

<p>> codebooks define how a (binary) file is organized.  An application may
> have to read the codebook first to correctly read the contents of the data
> file.
>
> To see how vorbis implements codebooks, take a look at vorbis/codebook.c
>
> > thanks for your answers,
> >
> > i am reading the specifications, and i  don't understand it all, i have
> > one
> > other question:
> >
> > i undestand the bitpacking operation.
> > but what about the codebook thing?
> > is it made for the decoder to know how the bit where packed, to know
what
> > are the lenght of the different entries stored in the bitstream?
> > i see that the codebook_entries is made to store the number of entries,
> > but
> > where is the size of the different entries stored in?
> >
> >
> > ----- Original Message -----
> > From: "Graham Mitchell" <graham at grahammitchell.com>
> > To: <vorbis at xiph.org>
> > Sent: Monday, September 22, 2003 12:27 PM
> > Subject: Re: [vorbis] bit rate
> >
> >
> >> > could someone give me the defintion of bitrate, and explain me why
the
> >> > bitrate is variable in vorbis?
> >>
> >> Beni gave an excellent explanation, but I should also plug my own
Vorbis
> >> introduction, which spends a fair amount of time discussing bitrates.
> >> http://grahammitchell.com/writings/vorbis_intro.html
> >>
> >> As to why it is variable in Ogg Vorbis, the short and sweet version is
> >> "because some passages are harder to encode than others, and it's
> >> foolish
> >> not to 'save' bits on easier sections so you can use them on tougher
> >> sections instead."
> >>
> >> --
> >> Graham Mitchell - computer science teacher, Leander High School
> >> "Christians and their opponents again and again expect that some new
> >> discovery will either turn matters of faith into matters of knowledge
or
> >> else reduce them to patent absurdities. But it has never happened. What
> >> we
> >> believe always remains intellectually possible; it never becomes
> >> intellectually compulsive. I have an idea that when this ceases to be
> >> so,
> >> the world will be ending."
> >> -- C.S. Lewis, from "Religion and Rocketry"
> >> --- >8 ----
> >> List archives:  http://www.xiph.org/archives/
> >> Ogg project homepage: http://www.xiph.org/ogg/
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>
> -------------------------------------------
> Karthik M
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