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

[Steve Underwood]

Denis Smirnov wrote:

>On Mon, Apr 17, 2006 at 07:27:04PM +0800, Steve Underwood wrote:
>
>SU> That is a slightly different issue, as it involves rate changes. 
>SU> However, it really doesn't make sense to do this in practice, though. 
>SU> The two ends should negotiate to use a common variant of Speex. 
>SU> Transcoding between variants is silly. Even when there are branches in 
>SU> the path, such as with conferencing, it doesn't really seem like much of 
>SU> a gain.
>
>Transcoding between variants can appear, if we have recordings (for voice
>prompts) in ultra wideband version (32k), and would play to phones, that
>support only low-rate codec version (16k).
>
>For speex this transcoding cheaper, then uwb<->sln<->wb transcoding.
>  
>
True. That is a valid situation. However, the computational cost is not 
the major issue. The quality of the converted audio will be far superior 
in a case like the one you mention if its done directly. Decoding and 
recoding low bit rate codecs is really bad news for quality. In the 
Speex case this is avoided completely when a direct rate conversion occurs.

Steve