Most codecs do not have any configurable parameters—they are what they are, and that’s all they are.
Some codecs, however, are capable of behaving in different ways. This primarily means that they can be optimized for a particular goal, such as cutting down on latency, making best use of a network, or perhaps delivering high quality.
The codecs.conf file is fairly new in Asterisk, and as of this writing it allows configuration of Speex parameters only. The settings are self-explanatory, as long as you are familiar with the Speex protocol (see http://www.speex.org).
codecs.conf also allows you to configure
Packet Loss Concealment (PLC). You need to define a
[plc] section and indicate
genericplc => true. This will cause
Asterisk to attempt to interpolate any packets that are missed.
(Enabling this functionality will incur a small performance