Media Control

The tapi32.dll can request the execution of a limited set of media control operations on the call's media stream triggered by telephony events. Although the tapi32.dll clients normally use the media function specifically defined for the media mode, media control can yield a significant performance improvement for client/server implementations because simple "detect/control" sequences can be offloaded to the server. The operation TSPI_lineSetMediaControl allows tapi32.dll to specify a list of tuples specifying a telephony event and the associated media-control action, and thus sets up a call's media stream for media control. The telephony events that can trigger media control activities are:

Detection of a digit The tapi32.dll provides a list of specific digits and the media control action each of them triggers.
Detection of a media mode The tapi32.dll provides a list of media modes and the media control actions a transition into the media mode triggers.
Detection of a specified tone The tapi32.dll specifies a list of tones and the media control action each tone detection triggers.
Detection of a call state The tapi32.dll specifies a list of call states and the media control action each transition to the call state triggers.

The following media control actions 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 (speed) of the media stream by an implementation-defined amount.
Rate normal Returns the rate (speed) to normal.
Volume up Increases the volume (amplitude) of the media stream.
Volume down Decreases the volume (amplitude) of the media stream.
Volume normal Returns the volume (amplitude) to normal.

The scope of media control is bounded 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.