Microsoft Unified Tuning Model Objects

Tuning Space Objects

A tuning space represents a particular type of network, along with other information that identifies a particular network provider or broadcast source. Microsoft provides four default tuning spaces; third parties may add their own tuning space. Tuning spaces are stored in the system registry. The SystemTuningSpaces object, which supports ITuningSpaceContainer, is used to create new tuning spaces or access existing ones.

Tune Request Objects

Tune requests encapsulate all the information needed to tune to a specified program. They are the created by a guide store loader component, stored in the Guide Store, retrieved by applications, and passed to either the Video Control (Windows® XP Home Edition and Windows XP Professional) or the Network Provider (Windows 9.x and Windows 2000). are created through a call to ITuningSpace::CreateTuneRequest. Applications generally will not create their own tune requests, but will obtain them from the Guide Store.

Stream Component Objects

A "component" in the context of digital television refers to an elementary stream within an MPEG-2 program stream. For example, a program stream may have three audio components, one in English, one in Spanish, and one in French. The actual components being provided by a service in some cases can only be discovered after reception begins. The Transport Information Filter (TIF) works with the Network Provider to fill in the component data in the tune request after tuning has occurred. The application can then examine the tune request, for example to inform the user of additional audio streams that are available.

Locator Objects

Locator objects contain low-level information that a tuner and Network Provider use to locate a program within a tuning space. This information includes the frequency and modulation type of the television signal, Quadrature Phase Shift Keying (QPSK) symbol rate, the type of forward error correction used, and other parameters specific to the network type. Each tune request contains a locator object, although it is not always necessary that all properties of the locator be set. A third party such as a cable or satellite provider may provide a default locator for their tuning space, which a Guide Store loader can use when creating tune requests. Locators are typically not used by applications, except perhaps for debugging purposes, or in the case where an application creates its own tune request.