[SIPForum-discussion] Different types of G729 codec

Steve Underwood steveu at coppice.org
Thu Aug 29 13:55:34 UTC 2013

On 08/28/2013 11:06 PM, Waqas Arshad wrote:
> Hi,
> Can someone please tell me the difference between following codecs in 
> detail and their compatibility with each other?
> g729
> g729a
> g729b
> g729ab
> g729 annexa=yes
> g729 annexa=no
> g729 annexb=yes
> g729 annexb=no
> I'll highly appreciate the responses.
> Regards
> Waqas
G.729 is the original codec. This never really caught on. You don't see 
it used very often.

G.729A is a revised codec, which is the really popular one. It gives 
poorer quality than the
original, but takes about half the compute power. The market said low 
compute beat high
quality. This is bit stream compatible with G.729, so it is not tagged 
differently in SDP or anywhere
else I know of.

G.729B is an add on to either of the above, which provides silence 
suppression and comfort noise

You can also have G.729C (G.729 implemented in floating point), G.729D 
(a 6.4kbps mode, with less than stellar quality, and rarely used), or 
G.729E (an 11.8kbps mode with better quality, but rarely used).

g729 is how G.729 and G.729A are tagged in SDP.

g729 annexb=yes is how G.729 and G.729A are tagged in SDP when the 
silence suppression scheme is enabled.

There is still buggy kit around which tags the SDP in other ways (e.g. 


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