[asterisk-dev] iLBC packet loss concealment (was: code-cleanup concerns)

[Steve Underwood]

Denis Smirnov wrote:

>On Mon, Apr 17, 2006 at 09:30:30AM +0800, Steve Underwood wrote:
>
>SU> Internally Asterisk uses 16 bit samples of signed linear audio at 8k 
>SU> samples per second. This is 128kbps, not 64kbps. Right now any codec is 
>SU> converted to this during transcoding. This is a bad thing. It ties 
>SU> Asterisk to 4kHz bandwidth. It is something that needs fixing.
>
>transcode_via_sln, that used by default, is a VeryBadThing (tm)
>  
>
I think very bad is overstating it. However, its not right. The ITU 
specs define specific ways to go ulaw->alaw->ulaw and 
ulaw->G.726->alaw->G.726->ulaw, and those are not followed. If they 
were, tandem operation would be better. I'm not sure that is a huge 
issue, though. Most of the transcoding is for things like G.729 or 
Speex, where the only way is via 16 bit linear audio.

Steve