[speex-dev] draft-herlein-speex-rtp-profile-01

[Jean-Marc Valin]

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.

        Jean-Marc

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 
> codec.
> 
> 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
> 
> 
> Tom Grandgent (tgrand at canvaslink.com) wrote:
> > 
> > Hi,
> > 
> > I have a question about section 3.4 of the RTP payload draft:
> > 
> > > Speex codecs [11] 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
> 
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-- 
Jean-Marc Valin, M.Sc.A.
LABORIUS (http://www.gel.usherb.ca/laborius)
Université de Sherbrooke, Québec, Canada

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