Speex dev - Feb 2011 - Speex - frame size & packet loss concealment

Hi all,

I am developing a VoIP application and have used SPEEX for that purpose; I
successfully managed to port the codec in fixed-point to an ADSP-21364
processor, and the codec works fine in narrowband, wideband and ultra-wideband
mode. Currently, I have chosen, in accordance with the speex manual, a 20 ms
frame size in each of these modes: in other words, the input buffer for speex
was set to respectively 160 - 320 - 640 samples. Now, I was wondering whether it
is possible to reduce this buffer size in order to reduce the latency of the
codec. Is this actually possible, or should I leave it as is? In addition, I
have another question regarding packet loss concealment. In the manual, I found
the encoder can be optimized for a certain percentage of packet loss by means of
the SPEEX_SET_PLC_TUNING parameter. What exactly does that optimization mean?
Does it mean the speex decoder will use some kind of packet loss concealment
algorithm to compensate for lost or late packets? And if so, what kind of packet
loss concealment scheme does speex use?

Best regards,

Peter
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