[asterisk-dev] New codec support in Asterisk 10

[Tilghman Lesher]

On Fri, Oct 14, 2011 at 11:53 AM, Jason Parker <jparker at digium.com> wrote:
> In Asterisk 10, we've changed the way codecs are defined, to expand the number
> of codecs that we can support.  However, due to protocol limitations, many
> channel drivers (pretty much everything but chan_sip) can only support a limited
> number of codecs.  As an example, chan_iax2 uses a 32-bit bitfield on the wire,
> which means the codec list on each side can never change.

One small correction:  chan_iax2 uses a 64-bit bitfield on the wire,
with approximately
30 of those bits unallocated.  (Testlaw can be removed; it's just a
duplicate of ulaw.)

> As it stands now, chan_iax2 will silently ignore allow=silk24 in iax2.conf.
> This issue has probably always existed in other channel drivers.  chan_skinny
> currently only supports 7 codecs; other codecs are ignored.

It would probably be helpful to allocate several of those codec bits
in IAX2 to "user-defined" and allow particular IAX2 networks to define
how those particular UD bits are used.  I agree that it's problematic
to allocate codecs to those bits, but there's certainly some leeway to
allow IAX2 to recognize some of the more popular codecs.