[asterisk-dev] default format for sounds

[Tzafrir Cohen]

On Sun, Sep 21, 2008 at 07:10:45PM +0200, Pavel Jezek wrote:
> 
> 
> 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.
> >
> >   
> imho, most people is using asterisk with sip phones over wan, so we need 
> common low bitrate codec,
> and it seems, that g729 will be optimal - good quality, require low 
> bandwith and almost all hw phones support it (except free softphones)
> PJ

Some will want gsm. Some will want g729. Some will want ilbc. Some will
want speex. 

Transcoding from one compressed format to another only reduces audio
quality. Furthermore, doing so at run-time takes extra CPU. If you know
you'll use it in your installation, sure install it. But this is not
good as a default.

g729 is particular is a non-option, as the default install cannot play
it.

-- 
               Tzafrir Cohen
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