[Speex-dev] Regarding mismatch in data rates of speex codec
ipse.speex at gmail.com
Thu May 31 03:30:55 PDT 2007
On 5/31/07, Jean-Marc Valin <jean-marc.valin at usherbrooke.ca> wrote:
> T Murali Mohan wrote:
> > Accoring to the Table.8.1 and Table.8.2 of speex manual (Version 1.2
> > Beta 2), the
> > data rates supported by speex codec for narrowband are *3.95, 5,95 ,8
> > ,11 ,15 ,18.2 and 24.6kbps*.
> > But when I run the code(downloaded from www.speex.org
> > <http://www.speex.org>), I am getting data rates of
> > *4,6,8,11.2,15,2,18.4 and 24.8 kbps.*
> > **
> > That is, for an input of 20ms frame the number of output bits I am
> > getting are *80,120,160,224,304,368 and 496* whereas
> > the number of bits given in the Table.8.1 are *79, 119, 160, 220, 300,
> > 364 and 492 .*
> > **
> > Can anybody help me in finding out the reason behind this mismatch.
> Easy. Most of the time when you're encoding, the number of bits gets
> rounded up to the next full byte. However, if you were to pack 8 frames
> in a packet, you'd see the same values as the manual has.
I think it's a common misunderstanding, so wouldn't it be nice to have
a "Note: " with warning about rounding to 8 bits and/or table or column in
existing table with values for 20ms frames. It may be helpful for people
who just want use Speex.
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