Which codecs should I choose for devices
It depends.
What codecs are supported?
Audio:
- G.711 A-law
- G.711 u-law
- G.723.1
- G.726
- G.729
- GSM
- iLBC
- LPC10
- Speex
- ADPCM
- 16 bit Signed Linear PCM
Video:
- H.261
- H.263
- H.263+
- H.264
Audio codecs
Most commonly used are:
- G711
- G729
G711
PSTN quality codec which is supported in 99% of all devices/providers (but often disabled to save traffic).
It has best quality but highest bandwidth (64kbps + ~20 kbps overhead ~= 84kbps to one direction).
It comes in 2 flavours - G711u (ulaw) - used in USA, and G711a (alaw) - used mostly in Europe and other countries.
G729
Little worse quality but is often used because it saves traffic (~8kbps + ~20kbps overhead ~= 28kbps to one direction).
It takes a lot of CPU power to transcode so total call count on the server is greatly reduced using this codec.
It needs to be installed separately and it is not free.
Video
Read manual for your device to check which codec is supported on your device.
H263/H264 are most popular.
Make sure same codec is chosen between devices you are trying to communicate.
Fax
If your system/provider/devices does not support T38 you should use G711 codec for fax transmitting/receiving.
Notes
Make sure you have always selected audio codec! Otherwise you will not be able to place calls!
