Asterisk Codec

VoIP 常用编码包括 ITU-T 系列的 G.7xx, GSM, iLBC
- 其它编码, speex 等已经不推荐使用
Asterisk codecs
G.729
- 需要版权, 默认只能透传
G.711
- ulaw
  - US
- alaw
  - Europe
iLBC
- Internet low Bitrate Codec
格式 - 优先选择 slin
- slin: 16 bit Signed Linear PCM
- gsm: 原始 GSM 编码，适用于 VoIP
- wav: MS wav format, 16 bit linear
- WAV: MS wav format, gsm encoded (wav49)
目前很多场景也推荐使用 Opus 编码
- 开源、高效、支持的平台多
参考
- Convert WAV audio files for use in Asterisk

# 查看编码、转译、文件格式
core show codecs
core show translation
core show file format

codec	name	ref
ADPCM, IMA
AMR	Adaptive Multi-Rate	RFC4867
AMR-WB
AMR-WB+
B64
G.722
G.723
G.726
G.729
GSM
H.264		RFC6184
H.265/HEVC	High Efficiency Video Coding	RFC7798
Opus		RFC7587
PCMA-WB	ITU-T G.711.1 A-law	RFC5391
PCMA,A-Law,alaw	ITU-T G.711 PCM A-Law	RFC3551
PCMU-WB	ITU-T G.711.1 μ-Law	RFC5391
PCMU,μ-Law,ulaw	TU-T G.711 PCM μ-Law	RFC3551
Speex

实时语音基本都是 20ms
RTCP NTP timestamp
- 1–60 samples per second.

VoIP 常用编码

以下编码时钟频率均为 8000, 默认包大小 20

Codec	PT	Note
PCMU	0	G.711/ulaw
GSM	3
G723	4
PCMA	8	G.711/alaw
G722	9
G729	18	G.729a

PT = RTC Payload Type

RTP payload formats

音频编码

最佳兼容编码是 ulaw、alaw、gsm
- allow=ulaw,alaw,g722
- disallow=all
开启 all 目前得到的是 codec2|g723|ulaw|alaw|gsm|g726|g726aal2|adpcm|slin|slin|slin|slin|slin|slin|slin|slin|slin|lpc10|g729|speex|speex|speex|ilbc|g722|siren7|siren14|testlaw|g719|opus|jpeg|png|h261|h263|h263p|h264|mpeg4|vp8|vp9|red|t140|t38|silk|silk|silk|silk
如果两端的编码不一致会由 asterisk 进行转码 - 有一定的性能影响
如果和允许的编码不匹配会导致拒绝
- SDP: Incompatible media format: no common codec
SDP 里的 rtpmap 标示支持的编码格式

SDP 头里的编码信息

m=audio 55560 RTP/AVP 0 101 3 8 110 97
a=rtpmap:101 telephone-event/8000
a=fmtp:101 0-16
a=rtpmap:110 speex/8000
a=rtpmap:97 iLBC/8000
a=fmtp:97 mode=30

编码类型
- u-law
- G726
- Speex Wide
- Speex Ultra
- Opus Narrow
- Opus Super
- Opus Full
- Opus Wide
- GSM
- a-law
- Speex Narrow
- iLBC 30
- G729
- G722

Coded	Fidelity	Bitrate
GSM	8000	13200
Opus	48000	6000 - 510000

视频编码

H.263 90Kbps
H.264
VP8
客户端支持情况
- XLite 支持 H263 H263P
- Zoiper 免费版支持 VP8 付费版支持 H264

音频文件转码

在线转码
- 支持转出 8K WAV、GSM、slin16、G729
Asterisk Sound Files 101!

# 如果出现警告, 可以尝试降低音量  -v 0.96
sox callwait.mp3 -c 1 -r 16000 -b 16 callwait.wav

批量转换

sox SilentCity.mp3 -t raw -r 8000 -s -2 -c 1 SilentCity.sln
cp *.sln /var/lib/asterisk/moh
asterisk -rx "module reload res_musiconhold.so"

# exten => 664,1,NoOp()
#     same => n,Progress()
#     same => n,MusicOnHold()

lame --decode music.mp3 music.wav
sox -V music.wav -r 8000 -c 1 -w music.raw
sox -V music.wav -r 8000 -c 1 -w music.gsm

for i in *.wav; do \
sox $i -r 8000 -c 1 $(basename $i .wav).raw; \
sox $i -r 8000 -c 1 $(basename $i .wav).gsm; \
done
rm *.wav

格式之间的转码时间

         Translation times between formats (in microseconds) for one second of data
          Source Format (Rows) Destination Format (Columns)

           ulaw  alaw   gsm  g726 g726aal2 adpcm  slin  slin  slin  slin  slin  slin  slin  slin  slin lpc10  ilbc  g722 testlaw
     ulaw     -  9150 15000 15000    15000 15000  9000 17000 17000 17000 17000 17000 17000 17000 17000 15000 15000 17250   15000
     alaw  9150     - 15000 15000    15000 15000  9000 17000 17000 17000 17000 17000 17000 17000 17000 15000 15000 17250   15000
      gsm 15000 15000     - 15000    15000 15000  9000 17000 17000 17000 17000 17000 17000 17000 17000 15000 15000 17250   15000
     g726 15000 15000 15000     -    15000 15000  9000 17000 17000 17000 17000 17000 17000 17000 17000 15000 15000 17250   15000
 g726aal2 15000 15000 15000 15000        - 15000  9000 17000 17000 17000 17000 17000 17000 17000 17000 15000 15000 17250   15000
    adpcm 15000 15000 15000 15000    15000     -  9000 17000 17000 17000 17000 17000 17000 17000 17000 15000 15000 17250   15000
     slin  6000  6000  6000  6000     6000  6000     -  8000  8000  8000  8000  8000  8000  8000  8000  6000  6000  8250    6000
     slin 14500 14500 14500 14500    14500 14500  8500     -  8000  8000  8000  8000  8000  8000  8000 14500 14500 14000   14500
     slin 14500 14500 14500 14500    14500 14500  8500  8500     -  8000  8000  8000  8000  8000  8000 14500 14500  6000   14500
     slin 14500 14500 14500 14500    14500 14500  8500  8500  8500     -  8000  8000  8000  8000  8000 14500 14500 14500   14500
     slin 14500 14500 14500 14500    14500 14500  8500  8500  8500  8500     -  8000  8000  8000  8000 14500 14500 14500   14500
     slin 14500 14500 14500 14500    14500 14500  8500  8500  8500  8500  8500     -  8000  8000  8000 14500 14500 14500   14500
     slin 14500 14500 14500 14500    14500 14500  8500  8500  8500  8500  8500  8500     -  8000  8000 14500 14500 14500   14500
     slin 14500 14500 14500 14500    14500 14500  8500  8500  8500  8500  8500  8500  8500     -  8000 14500 14500 14500   14500
     slin 14500 14500 14500 14500    14500 14500  8500  8500  8500  8500  8500  8500  8500  8500     - 14500 14500 14500   14500
    lpc10 15000 15000 15000 15000    15000 15000  9000 17000 17000 17000 17000 17000 17000 17000 17000     - 15000 17250   15000
     ilbc 15000 15000 15000 15000    15000 15000  9000 17000 17000 17000 17000 17000 17000 17000 17000 15000     - 17250   15000
     g722 15600 15600 15600 15600    15600 15600  9600 17500  9000 17000 17000 17000 17000 17000 17000 15600 15600     -   15600
  testlaw 15000 15000 15000 15000    15000 15000  9000 17000 17000 17000 17000 17000 17000 17000 17000 15000 15000 17250       -

音频文件编码格式说明

ID	TYPE	NAME	FORMAT	DESCRIPTION
31	image	png	png	(PNG Image)
6	audio	g726	g726	(G.726 RFC3551)
4	audio	alaw	alaw	(G.711 a-law)
2	audio	g723	g723	(G.723.1)
20	audio	speex	speex	(SpeeX)
21	audio	speex	speex16	(SpeeX 16khz)
22	audio	speex	speex32	(SpeeX 32khz)
24	audio	g722	g722	(G722)
25	audio	siren7	siren7	(ITU G.722.1 (Siren7, licensed from Polycom))
32	video	h261	h261	(H.261 video)
33	video	h263	h263	(H.263 video)
8	audio	adpcm	adpcm	(Dialogic ADPCM)
43	audio	silk	silk8	(SILK Codec (8 KHz))
44	audio	silk	silk12	(SILK Codec (12 KHz))
45	audio	silk	silk16	(SILK Codec (16 KHz))
46	audio	silk	silk24	(SILK Codec (24 KHz))
28	audio	g719	g719	(ITU G.719)
34	video	h263p	h263p	(H.263+ video)
35	video	h264	h264	(H.264 video)
19	audio	g729	g729	(G.729A)
9	audio	slin	slin	(16 bit Signed Linear PCM)
10	audio	slin	slin12	(16 bit Signed Linear PCM (12kHz))
11	audio	slin	slin16	(16 bit Signed Linear PCM (16kHz))
12	audio	slin	slin24	(16 bit Signed Linear PCM (24kHz))
13	audio	slin	slin32	(16 bit Signed Linear PCM (32kHz))
14	audio	slin	slin44	(16 bit Signed Linear PCM (44kHz))
15	audio	slin	slin48	(16 bit Signed Linear PCM (48kHz))
16	audio	slin	slin96	(16 bit Signed Linear PCM (96kHz))
17	audio	slin	slin192	(16 bit Signed Linear PCM (192kHz))
3	audio	ulaw	ulaw	(G.711 u-law)
18	audio	lpc10	lpc10	(LPC10)
27	audio	testlaw	testlaw	(G.711 test-law)
42	audio	none	none	(Null codec)
41	image	t38	t38	(T.38 UDPTL Fax)
38	video	vp9	vp9	(VP9 video)
37	video	vp8	vp8	(VP8 video)
5	audio	gsm	gsm	(GSM)
36	video	mpeg4	mpeg4	(MPEG4 video)
23	audio	ilbc	ilbc	(iLBC)
39	text	red	red	(T.140 Realtime Text with redundancy)
40	text	t140	t140	(Passthrough T.140 Realtime Text)
29	audio	opus	opus	(Opus Codec)
30	image	jpeg	jpeg	(JPEG image)
7	audio	g726aal2	g726aal2	(G.726 AAL2)
1	audio	codec2	codec2	(Codec 2)
26	audio	siren14	siren14	(ITU G.722.1 Annex C, (Siren14, licensed from Polycom))

文件格式说明

| Format | Name | Extensions | | ------- | ------- | ---------- | ------ | --- | --- | --- | | slin192 | sln192 | sln192 | | slin96 | sln96 | sln96 | | slin48 | sln48 | sln48 | | slin44 | sln44 | sln44 | | slin32 | sln32 | sln32 | | slin24 | sln24 | sln24 | | slin16 | sln16 | sln16 | | slin12 | sln12 | sln12 | | slin | sln | sln | raw | | gsm | gsm | gsm | | g719 | g719 | g719 | | g729 | g729 | g729 | | g726 | g726-16 | g726-16 | | g726 | g726-24 | g726-24 | | g726 | g726-32 | g726-32 | | g726 | g726-40 | g726-40 | | slin16 | wav16 | wav16 | | slin | wav | wav | | h264 | h264 | h264 | | h263 | h263 | h263 | | siren7 | siren7 | siren7 | | ilbc | iLBC | ilbc | | g723 | g723sf | g723 | g723sf | | g722 | g722 | g722 | | ulaw | au | au | | alaw | alaw | alaw | al | alw | | ulaw | pcm | pcm | ulaw | ul | mu | ulw | | siren14 | siren14 | siren14 | | gsm | wav49 | WAV | wav49 | | adpcm | vox | vox |

VoIP 常用编码​

音频编码​

视频编码​

音频文件转码​

批量转换​

格式之间的转码时间​

音频文件编码格式说明​

文件格式说明​