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

[Tom Grandgent]

Ohh...  Nice!  This is new in 1.0.1, isn't it?  It doesn't seem to 
be included in the reference manual yet, though.

Thanks!

Tom

<p>Jean-Marc Valin (jean-marc.valin at hermes.usherb.ca) wrote:
> 
> 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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