The mixer interface provides a uniform way to control the volume on a hardware (or software) mixer. The interface is primarily intended to be implemented by elements for audio inputs and outputs that talk directly to the hardware (e.g. OSS or ALSA plugins).
Using this interface, it is possible to control a list of tracks (such as Line-in, Microphone, etc.) from a mixer element. They can be muted, their volume can be changed and, for input tracks, their record flag can be set as well.
Example plugins implementing this interface include the OSS elements (osssrc, osssink, ossmixer) and the ALSA plugins (alsasrc, alsasink and alsamixer).