[asterisk-dev] default format for sounds

[Alex Balashov]

I would say ulaw is the most common denominator, as it seems to me that 
G.711u is the most parsimonious and ubiquitous use case and G.711u is 
the standard-bearer of native PCM.  A-law could also work.

Everything else is overly specialised.  There should definitely not be 
much, if any transcoding involved for default scenarios.

The other thing is that if someone does want to convert all their 
prompts and recordings to some other format more compatible with their 
configuration, the prompts need to be of the highest quality possible as 
a departure point for any conversion or transcoding.  G.711u/A are 
uncompressed 64 kbps / 8 KHz streams.  Everything else is varying 
degrees of lossy compression.  I definitely would not distribute those 
recordings using a CELP or other intensely approximated codec.


Tzafrir Cohen wrote:

> Hi
> 
> The default format for sounds files is currently GSM. This is done in
> the interest of backward-compatibility. However it maens that by default
> we get sound of lower quality and with more work by the CPU.
> 
> I think it would be nice to switch to a different format (by default).
> 
> Switch to a different format rather than just enable a different format:
> I suppose that the point of using GSM is to save space. If you suddenly
> enable a new format, you lose that benefit.
> 
> * Except those who actually use GSM, and will now have to pay extra CPU.
>   GSM encoding is more expensive than GSM decoding.
> * But I suspect that those are generally a minority, and most will
>   benefit.
> 
> Which will be the default format?
> 
> Possible contenders:
> 1. One of alaw/ulaw. A good balance of size and CPU load, assuming 8kHz
>    sample rate. This is a raw format and hence can be easily
>    concatenated.
> 2. slin. Does it actually give a better quality than alaw/ulaw? It takes
>    more space.
> 3. wav - Unlike slin, this is not a raw format, and hence can be easily
>    be played (tested) by other players.
> 4. slin16: If we don't want to assume 8kHz sample rate all over.
> 


-- 
Alex Balashov
Evariste Systems
Web    : http://www.evaristesys.com/
Tel    : (+1) (678) 954-0670
Direct : (+1) (678) 954-0671
Mobile : (+1) (706) 338-8599