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Overview of Media Support

Asterisk supports a variety of audio and video media. Asterisk provides CODEC modules to facilitate encoding and decoding of audio streams. Additionally file format modules are provided to handle writing to and reading from the file-system.

The tables on this page describe what capabilities Asterisk supports and specific details for each format.

On This PageEnabling specific media support

There are three basic requirements for making use of specific audio or video media with Asterisk.

  1. The Asterisk core must support the format or a module may be required to add the support.
  2. Asterisk configuration must be modified appropriately.
  3. The devices interfacing with Asterisk must support the format and be configured to use it.

Module compilation and loading

For audio or video capabilities that require a module - you should make sure that the module is built and installed on the system.

See the section on Using Menuselect to Select Asterisk Options if you need help figuring out how to get a module built and then section on Configuring the Asterisk Module Loader to verify that a module gets loaded when Asterisk starts up.

Channel driver configuration

Audio or video capabilities for Asterisk are used on a per channel or per feature basis. To tell Asterisk what CODECs or formats to use in a particular scenario you may need to configure your channel driver, or modify configuration for the feature itself.

We'll provide two examples, but you should look at the documentation for the channel driver or feature to better understand how to configure media in that context.

Configuring allowed media for a PJSIP endpoint



We set the option "allow" to a string of values "!all,ulaw".

  • The value "!all" means "Disallow all" and is identical to "disallow=all". This tells Asterisk to disallow all codecs except what we further define in the allow option.
  • The value "ulaw" instructs Asterisk to allow ulaw audio during media negotiation for this endpoint.

See the section Configuring res_pjsip for more information on the PJSIP channel driver.

Configuring app_voicemail file formats for recordings



In the general section of voicemail.conf you can set the formats used when writing voicemailto the file-system. We set the option "format" to a string of file format names.

  • The value "wav49" represents GSM in a WAV|wav49 container.
  • The value "wav" represents SLIN in a wav container.
  • The value "gsm" represents GSM in straight gsm format.

Endpoint device configuration

Configuring your particular device is outside the scope of the Asterisk documentation.

Consult your devices user/admin manual to find out where you define codecs or media to be used.

For VoIP desk phones there are typically two places to look for media configuration.

  1. The web GUI for the phone.
  2. The provisioning files that are pulled down by the phones on your network.

Audio Support

A variety of audio capabilities are supported by Asterisk.

Name Config Value Capability:(P)assthrough CODEC Module Format Module Distributed w/ Asterisk? Commercial License
ADPCM adpcm T codec_adpcm format_vox YES NO
G.711 A-law alaw T codec_alaw format_pcm YES NO
G.711 ยต-law ulaw T codec_ulaw format_pcm YES NO
G.719 g719 P n/a format_g719 YES NO
G.722 g722 T codec_g722 format_pcm YES NO
G.722.1 Siren7 siren7 T codec_siren7 format_siren7 Codec(NO) Format(YES) NO
G.722.1C Siren14 siren14 T codec_siren14 format_siren14 Codec(NO) Format(YES) NO
G.723.1 g723 T codec_g723 format_g723 Codec(NO) Format(YES) YES(hardware required)
G.726 g726 T codec_g726 format_g726 YES NO
G.726 AAL2 g726aal2 T codec_g726 format_g726 YES NO
G.729A g729 T codec_g729a format_g729 Codec(NO) Format(YES) YES
GSM gsm T codec_gsm format_gsm YES NO
ILBC ilbc T codec_ilbc format_ilbc YES NO
LPC-10 lpc10 T codec_lpc10 n/a YES NO
SILK silk T codec_silk n/a Codec(NO) Format(YES) NO
Speex speex T codec_speex n/a YES NO
Signed Linear PCM slin T codec_resample format_sln YES NO
Ogg Vorbis n/a n/a n/a format_ogg_vorbis Codec(NO) Format(YES) NO
Opus opus T codec_opus n/a Codec(NO) Format(YES) NO
wav (SLIN) wav T n/a format_wav YES NO
WAV (GSM) wav49 T n/a format_wav_gsm YES NO

Speex Support

Asterisk supports 8, 16, and 32kHz Speex. Use of the 32kHz Speex mode is, like the other modes, controlled in the respective channel driver's configuration file, e.g. chan_sip's sip.conf or PJSIP's pjsip.conf.

Signed Linear PCM

Asterisk can resample between several different sampling rates and can read/write raw 16-bit signed linear audio files from/to disk. The complete list of supported sampling rates and file format is found in the expansion link below:

Sampling Rate Asterisk File format
8kHz .sln
12kHz .sln12
16kHz .sln16
24kHz .sln24
32kHz .sln32
44.1kHz .sln44
48kHz .sln48
96kHz .sln96
192kHz .sln192


Users can create 16-bit Signed Linear files of varying sampling rates from WAV files using the sox command-line audio utility.

sox input.wav -t raw -b 16 -r 32000 output.sln
mv output.sln output.sln32  


In this example, an input WAV file has been converted to Signed Linear at a depth of 16-bits and at a rate of 32kHz. The resulting output.sln file is then renamed output.sln32 so that it can be processed correctly by Asterisk.

Video and Image Support

You'll notice the CODEC module column is missing. Video transcoding or image transcoding is not currently supported.

Name Config Value Capability:(P)assthrough Format Module Distributed w/ Asterisk
JPEG jpeg P format_jpeg YES
H.261 h261 P n/a YES
H.263 h263 P format_h263 YES
H.263+ h263p P format_h263 YES
H.264 h264 P format_h264 YES
VP8 vp8 P n/a YES
VP9 vp9 P n/a YES