Codec

Codec	Sampling Rate (kHz)	Bandwidth (kbps)	Nominal Bandwidth (kbps)	Payload Size (ms)	License	Comments	Pros	Cons
DVI4	unknown	unknown	unknown			Not a very common codec.
G.711	8	64	87.2	20	Open Source	G.711u/a often refered to as u-law/a-law: where a-law is the European version and u-law the US/Japanese version	Designed to deliver precise transmission of speech Very low processing overheads	Including overheads, uses >64kbps, thus at least 128kbps bandwidth in each direction is required
G.722	16	48	unknown		Open Source	An ITU standard codec.
	16	56	unknown	30
	16	64	unknown
G.723.1	8	5.3	20.8	30	Proprietry	Often used by dialup VoIP users for optimal quality.	Very high compression whilst maintaining high quality audio.	Requires a lot of processor power.
G.723.1	8	6.3	21.9	30	Proprietry	Often used by dialup VoIP users for optimal quality.		Requires a lot of processor power.
G.726	8	16	unknown		Open Source	An improved version of G.721 and G.723 (totally different from G.723.1)		CPU overhead is relatively low for level of compression obtained.
	8	24	47.2	20
	8	32	55.2	20
	8	40	unknown
G.728	unknown	16	31.5		Open Source	An ITU standard codec.
G.729	8	8	31.2	20	Patented	An ITU standard codec.	Excellent bandwidth utilisation for toll quality speech Performs well under random bit errors	License required for use
GSM	8	13	unknown		Proprietry	Same encoding as used in GSM mobile phones (though improved version are often used nowadays).	Relatively high compression ratio. Royalty free means it is available in many hardware and software platforms.
iLBC	unknown	13.33	unknown	30	Free to use		High robustness to packet loss
iLBC	unknown	15	unknown	20	Free to use		High robustness to packet loss
Siren	unknown	unknown	unknown			Not much known about this codec, and does not appear to be commonly supported.
Speex	8	unknown	unknown		Open Source		Uses variable bit rate to minimise bandwidth usage
	16	unknown	unknown
	32	unknown	unknown