[Speex-dev] Quick survey for Speex 1.2

Jean-Marc Valin jean-marc.valin at usherbrooke.ca
Tue Nov 14 03:12:37 PST 2006

> 1) The voice quality of ouput after coding and decoding in WB mode is
> unacceptable using the SVN fixed-point code,
>    while the ouput of floating-point code is good.
> The test flow is input-->coder---->decoder---->.wav file--->player.
> The quality  decrease of the decoder output is notable to ears.
> according to above test, some fixed-point codes must need to be corrected.
> What's your experience with current fixed-point code?

Indeed, your file triggers a problem with the fixed-point code. It
doesn't happen with all files, so I'm not sure yet if it's a regression
(if you've tested with other versions, I'm interested in what you find).
I'll be investigating the issue and will fix this as soon as I can.
Thanks for reporting the problem.

> 2) The rtp profile is not clear
> In the svn directory /doc, draft-herlein-speex-rtp-profile-02.txt is the
> latest draft.
> According to the chapter 5,
>  "The encoding and decoding algorithm can change the bit rate at any 20
>   msec frame boundary, with the bit rate change notification provided
>   in-band with the bit stream.  Each frame contains both "mode"
>   (narrowband, wideband or ultra-wideband) and "sub-mode" (bit-rate)
>   information in the bit stream.  No out-of-band notification is
>   required for the decoder to process changes in the bit rate sent by
>   the encoder."
> The "sub-mode" can be calculated from the size of coded frame if "mode" is
> known.
> But the "mode" is not contained in the coding ouput (note it's not the ogg
> case) according to the source code.
> How does the decoder know the "mode" from RTP package?(it's assigned
> directly in the decoder in current svn sources)

The mode/bit-rate is detected automatically by the decoder because it's
encoded in the first few bits of each frame. The encoder can change
bit-rate at any time without telling the decoder. Can you be more
precise as to what isn't clear?

> What's the use of file rtp.txt in /doc directory? and its relationship with
> draft-herlein-speex-rtp-profile-02.txt?

The IETF stuff has been really, really slow. I'm still looking for
someone who knows enough to help me finalise all this.


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