[speex-dev] input format

Jean-Marc Valin jean-marc.valin at hermes.usherb.ca
Thu Feb 20 09:31:29 PST 2003

Le jeu 20/02/2003 à 12:21, X-Fixer a écrit :
> just to check that I've got everything right.
> the encoder allows as input
> - mono only

Well, there's support for simple stereo (intensity-based) encoding too,
but it's probably not necessary to take care of it now.

> - 8 or 16 bits as floating point numbers (without scaling to 1.0).
> floating-point wavs (IEEE) will also work, but it's better to scale
> them to something like 8000.

the speexenc/speexdec utility can deal with 8/16 bits, but the library
itself takes floating point values with max 32000 scaling (prefered
around 8000).

> - any sample rate (should be set with speex_encoder_ctl), but prefered
> are 8/16/32 kHz. but what modes should I use for a given rate?

8 kHz is narrowband (speex_nb_mode), 16 kHz is wideband (speex_wb_mode)
and 32 kHz is ultra-wideband (speex_uwb_mode)

> also
> - what bit rates are allowed?

Too many to list here: from around 2 kbps to 44 kbps

> - what's the difference between quality and complexity? complexity
> does not affect decoder speed while quality does?

complexity means: take more (or less) CPU to do a better job at
encoding. It doesn't change the bit-rate, but it has a (small) effect on
quality. Of course, the quality of the encoding is mainly controlled by
the "quality" parameter (which has a direct effect on bit-rate).

> also, to have a "legal" ACM codec one should register at microsoft
> (get MID, PID and format tag). is this somehow possible? I mean Xiph
> is a solid organization.

Might want to contact Emmett Plant <emmettfish at mac.com> about that
(contact me again if you don't get an answer).


Jean-Marc Valin, M.Sc.A.
LABORIUS (http://www.gel.usherb.ca/laborius)
Université de Sherbrooke, Québec, Canada

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