Media Control

An application can request the execution of a limited set of media-control operations on the call's media stream triggered by telephony events. Although an application is encouraged to use the media API specifically defined for the media mode, media control can yield a significant performance improvement for client/server implementations. The lineSetMediaControl function is used to set up a call's media stream for media control by allowing an application to specify a list of tuples specifying a telephony event and the associated media-control action. The telephony events that can trigger media-control activities are:

Detection of a digit. The application provides a list of specific digits and the media-control action that each of them triggers.
Detection of a media mode. The application provides a list of media modes and the media-control actions that a transition into the media mode triggers.
Detection of a specified tone. The application specifies a list of tones and the media-control action that each tone detection triggers.
Detection of a call state. The application specifies a list of call states and the media-control action that each transition to the call state triggers.

The media-control actions listed below are defined generically for the different media modes. Not all media streams can provide meaningful interpretations of the media-control actions. The operations should map well to audio streams:

Start starts the media stream.
Reset resets the media stream.
Pause stops or pauses the media stream.
Resume starts or resumes the media stream.
Rate up increases the rate (speed) of the media stream by an implementation-defined amount.
Rate down decreases the rate of the media stream by an implementation-defined amount.
Rate normal returns the rate to normal.
Volume up increases the volume (amplitude) of the media stream.
Volume down decreases the volume of the media stream.
Volume normal returns the volume to normal.

The scope of media control is bound by the lifetime of the call. Media control on a call ends as soon the call disconnects or goes idle. Only a single media-control request can be outstanding on a call across all applications.

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