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Component Property Functions and Selectors

Component property functions, which are available in QuickTime 6.4 and later, provide another way to get information about components. They can also be used to configure components without a user dialog, to configure a component programmatically, and to set up callbacks that are called when something changes in a component.

The configuration interface to many components, such as those used for capture, export, and compression, involves a standard user dialog. QuickTime-based applications sometimes need to configure these operations from custom user interfaces or to configure them programmatically, with no user interaction at all.

The following functions are available to work with component properties:

• QTGetComponentPropertyInfo gets information about a specified property of a component, such as the size and data format.

• QTGetComponentProperty gets the value of a specific component property.

• QTSetComponentProperty sets the value of a specific component property programmatically.

• QTAddComponentPropertyListener installs a callback to monitor a component property. Your callback function is called when the property value changes.

• QTRemoveComponentPropertyListener removes a component property monitoring callback.

• QTComponentPropertyListenerCollectionCreate creates a collection of component property monitors, allowing you to manage groups of callback functions.

• QTComponentPropertyListenerCollectionAddListener adds a listener callback for a specified property class and ID to a property listener collection.

• QTComponentPropertyListenerCollectionRemoveListener removes a listener callback with a specified property class and ID from a property listener collection.

• QTComponentPropertyListenerCollectionNotifyListeners calls all listener callbacks in a component property listener collection registered for a specified property class and ID.

• QTComponentPropertyListenerCollectionHasListenersForProperty determines if there are any listeners in a component property listener collection registered for a specified property class and ID.

• QTComponentPropertyListenerCollectionIsEmpty determines if a listener collection is empty.

Beginning with Quicktime 6.4, the Component Manager defines optional standard selectors for component properties. These selectors can be implemented by all components, regardless of type, that are written to work with the component properties mechanism. Components can adopt these functions on their own schedule. The Component Manager allows callers to discover safely whether components implement the property selectors and perform operations according to older mechanisms if support for the properties mechanism is unavailable.

As developers adopt the component property functions, it will be possible to configure most or all exporters, for example, by means of the same set of properties. Use of the component property functions allows support for richer scripting and simpler custom user interfaces.

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