Speex dev - Aug 2004 - auto-detection of frame boundary

Here's the situation: 3 frames are being transferred back to back over
RTP.  The total payload is known (thus the TOTAL frame size).  We'd like
to decode all 3.

 

According to IETF RTP Profile (appendix C, of Jean-Marc's Speex Codec
Manual, verison 1.0),  "it's only necessary to consider the sequence of
bits as output by the Speex encoder, and present the same sequence to
the decoder", I kind of got the impression that length-prefix PER FRAME
is not necessary, as long as speex_decode() is called 3 times.

 

Is this true ?

 

 

Thanks all,

 

 

Tongbiao Li

 

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> Hereÿs the situation: 3 frames are being transferred back to back over
> RTP.  The total payload is known (thus the TOTAL frame size).  Weÿd
> like to decode all 3. 
> 
> According to IETF RTP Profile (appendix C, of Jean-Marcÿs Speex Codec
> Manual, verison 1.0),  ´itÿs only necessary to consider the sequence
> of bits as output by the Speex encoder, and present the same sequence
> to the decoder¡, I kind of got the impression that length-prefix PER
> FRAME is not necessary, as long as speex_decode() is called 3 times.
>
> Is this true ?
That's right, if you call speex_encode 3 times, you can call
speex_decode 3 times. Note that you need to let Speex do the
concatenation of the frames. If you try to concatenate the bytes
yourself, you risk problems because sometimes the frames don't end a
byte boundary.

        Jean-Marc


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

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