jean-marc.valin at hermes.usherb.ca
Tue Jul 1 17:48:53 PDT 2003
OK, this is how it works:
The encoder calls speex_encode any number of times and then calls
speex_bits_insert_terminator before sending the bits.
The decoder then keeps calling speex_decode until it returns -1, which
means that the terminator is reached.
Le mar 01/07/2003 à 20:41, Tom Grandgent a écrit :
> Ok, I figured it out. :) This seems to work:
> 1) Call speex_bits_read_from() once, specifying the location in
> memory of the compressed data, and the total length of that data.
> 2) Keep calling speex_decode() until speex_bits_remaining()
> returns 0.
> Then you don't have to keep track of the # of frames per packet,
> or the size of each compressed frame. It's done magically by the
> I now see that in section 4.5 of SpeexManual.pdf it touches on this
> briefly, and mentions a terminator code. But, it's not quite clear
> as to how this terminator code is used... especially since it refers
> to figure 4 which doesn't seem to exist. (doc bug?)
> Might I humbly recommend a section of documentation elaborating on
> the use of the speex_bits*() calls ...
> Tom Grandgent (tgrand at canvaslink.com) wrote:
> > Hi,
> > I have a question about section 3.4 of the RTP payload draft:
> > > Speex codecs  are able to detect the the bitrate from the
> > > payload and are responsible for detecting the 20 msec boundaries
> > > between each frame.
> > This suggests that you can encode some frames with Speex, pass the
> > compressed bits to the decoder, and you'll get the output - without
> > having to do external bookkeeping for compressed frame size. (I'm
> > thinking of VBR here where compressed frame size varies constantly.)
> > If this is true, how does one go about leaving this responsibility to
> > the codec? It seems like I have to pass the size of the compressed
> > frame as the last parameter of speex_bits_read_from(), then call
> > speex_decode() to decode one frame at a time. This is how the sample
> > code in the manual works, and the reference manual doesn't shed any
> > light on this.
> > So basically, if I'm given an RTP packet with several back-to-back
> > VBR-compressed Speex frames, how do I decode it?
> > Thanks,
> > Tom
> --- >8 ----
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Jean-Marc Valin, M.Sc.A.
Université de Sherbrooke, Québec, Canada
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