[vorbis-dev] encoding to fixed window length vorbis file

[Emmett Plant]

Hey there!

Comment out line 202, 205 and 206 from envelope.c, recompile and encode a
44KHz stereo file. This will harm quality, but you probably already know
that.

Emmett Plant
CEO, Xiph.org Foundation

(Oh, I am so not this cool. Thanks go to Garf for the pick-up.)

On 1/9/03 1:30 PM, "c0g" <c0g at wp.pl> wrote:

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> Hi!
> I want to encode wav file into fixed window length vorbis file. I don't
> know if "window" is good name for that, but i mean MDCT buffer size.
> This buffer is passed to mdct_backward() as "in" and it's size is
> determined by "init->n" variable which is also passed to this function.
> So, when I say "window size" I mean "init->n" value.
> I noticed, that when decoding ogg vorbis file, window size is changing
> and it's values for normal quality sound are: mostly 1024, somethimes
> 512 and very rarely 256.
> I noticed also, that when decoding file resampled to 11kHz this value is
> always 512 (for files I tested). When I resampled to 5,5kHz there was no
> change in window size. I tried many combinations of oggenc options, but
> the lowest window size, I obtained was still 512.
> 
> But I want to make file with window size = 256.
> 
> Is there way to accomplish that?
> 
> And now, why I need this.
> I'm working on ogg vorbis decoder optimised for SUN SPARC machines. SUN
> provides library (medialib, mlib) of multimedia functions, which are
> written in VIS assembly, so they are fast. I want to optimise bacward
> MDCT, and use medialib function for it. But here is a problem: medialib
> IMDCT has hard-coded buffer size = 256. It is not possible to use it for
> larger buffers (I think - I tried to use it twice on two halfes of 512
> buffer on many ways). And the second problem is my project deadline is
> comming soon, so I want to make decoder that works only on files with
> windows size = 256 :P
> 
> Thanks in advance for any help!
> 
> - --
> c0g at wp.pl
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