Codecs and Formats

Codecs And Formats

Codecs translate audio frames. Formats read and write media files.

Codec Translators

Module	Source	Purpose
codec_opus.so	codecs/codec_opus.c	Opus coder/decoder using libopus.
codec_alaw.so	codecs/codec_alaw.c	A-law coder/decoder.
codec_ulaw.so	codecs/codec_ulaw.c	mu-law coder/decoder.
codec_a_mu.so	codecs/codec_a_mu.c	Direct A-law/mu-law conversion.
codec_g722.so	codecs/codec_g722.c	ITU G.722 transcoder.
codec_g726.so	codecs/codec_g726.c	ITU G.726 transcoder.
codec_gsm.so	codecs/codec_gsm.c	GSM coder/decoder.
codec_ilbc.so	codecs/codec_ilbc.c	iLBC coder/decoder.
codec_lpc10.so	codecs/codec_lpc10.c	LPC10 coder/decoder.
codec_speex.so	codecs/codec_speex.c	Speex coder/decoder.
codec_adpcm.so	codecs/codec_adpcm.c	ADPCM coder/decoder.
codec_resample.so	codecs/codec_resample.c	Signed linear resampling.
codec_dahdi.so	codecs/codec_dahdi.c	Generic DAHDI transcoder translator.

Opus

codec_opus is important for modern SIP and browser-oriented deployments.

Requirements:

libopus
pkg-config

Configuration:

configs/codecs.conf.sample

Example:

[opus]
bitrate => 32000
fec => true
dtx => false

Runtime:

*CLI> opus show

SIP peer example:

disallow=all
allow=opus
allow=alaw
allow=ulaw

File Format Modules

Module	Purpose
format_wav	Microsoft WAV/WAV16 signed linear.
format_wav_gsm	WAV with GSM.
format_pcm	Raw/Sun ulaw/alaw PCM and G.722.
format_sln	Raw signed linear audio.
format_sln16	Raw signed linear 16 kHz audio.
format_gsm	Raw GSM data.
format_g729	Raw G.729 data.
format_g726	Raw G.726 data.
format_g723	G.723.1 timestamp file format.
format_ilbc	Raw iLBC data.
format_g719	ITU G.719.
format_siren7	Siren7.
format_siren14	Siren14.
format_ogg_vorbis	OGG/Vorbis audio.
format_vox	Dialogic VOX ADPCM.
format_jpeg	JPEG image format.
format_h263	Raw H.263 video.
format_h264	Raw H.264 video.

Add-on Format

Module	Purpose
format_mp3	MP3 format add-on.

Media Troubleshooting

If there is one-way audio or failed negotiation:

• Check codec lists on both peers.
• Check RTP payload types in SIP debug.
• Keep directmedia=no while testing.
• Verify NAT settings.
• Verify transcoding modules are loaded.
• Verify format modules are loaded when playback/recording files fail.