[speex-dev] Speex SIP support in the "Asterisk" PBX, FYI

Jean-Marc Valin jean-marc.valin at hermes.usherb.ca
Tue Mar 11 20:12:45 PST 2003

> Unfortunately, the sampling frequency is also the RTP timestamp frequency, 
> so if Asterisk thinks that the stream is 8 kHz, but the Speex client thinks 
> that it's 16 kHz, then each side will probably misinterpret the RTP 
> timestamps sent by the other side.

Well, the timestamp will be the same. A wideband frame is a narrowband
frame with additional information to describe the high-band (4-8 kHz). A
narrowband decoder will just ignore that additional info, while a
wideband decoder will use it to produce 16 kHz. In all cases, the frames
are 20 ms.


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

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