# Asterisk Project : Codec Modules

Added by malcolmd , edited by mdavenport on Sep 06, 2012

CODEC modules have file names that look like codec_xxxxx.so, such as codec_alaw.so and codec_ulaw.so.

CODECs represent mathematical algorithms for encoding (compressing) and decoding (decompression) media streams. Asterisk uses CODEC modules to both send and recieve media (audio and video). Asterisk also uses CODEC modules to convert (or transcode) media streams between different formats.

CODEC modules have file names that look like codec_xxxxx.so, such as codec_alaw.so and codec_ulaw.so.

Asterisk is provided with CODEC modules for the following media types:

- ADPCM, 32kbit/s
- G.711 alaw, 64kbit/s
- G.711 ulaw, 64kbit/s
- G.722, 64kbit/s
- G.726, 32kbit/s
- GSM, 13kbit/s
- LPC-10, 2.4kbit/s

If the Speex (www.speex.org) development libraries are detected on your system when Asterisk is built, a CODEC module for Speex will also be installed.

If the iLBC (www.ilbcfreeware.org) development libraries are detected on your system when Asterisk is built, a CODEC module for iLBC will also be installed.

Support for the patent-encumbered G.729A or G.723.1 CODECs is provided by Digium on a commercial basis through both software and hardware products. For more information about purchasing licenses or hardware to use the G.729A or G.723.1 CODECs with Asterisk, please see Digium's website.

Support for Polycom's patent-encumbered but free G.722.1 Siren7 and G.722.1C Siren14 CODECs, or for Skype's SILK CODEC, can be enabled in Asterisk by downloading the binary CODEC modules from Digium's website.

For more detailed information on CODECs, see CODECs.