Creating Timeline Objects

Microsoft DirectShow 9.0

Creating Timeline Objects

The sample code presented in this article starts with an empty timeline, but the same steps apply if you load an existing project and want to add objects to it.

To create any type of object in the timeline, call the IAMTimeline::CreateEmptyNode method. For example, the following code creates a new group:

IAMTimelineObj *pGroupObj = NULL;
pTL->CreateEmptyNode(&pGroupObj, TIMELINE_MAJOR_TYPE_GROUP);

The second parameter is a member of the TIMELINE_MAJOR_TYPE enumeration. It specifies the type of timeline object to create, such as a group or a track.

The CreateEmptyNode method creates the object and returns a pointer to the object's IAMTimelineObj interface. It also increments the reference count on the IAMTimelineObj interface, so you must release the interface when you finish using it. Do not call the CoCreateInstance function. Instead, always use CreateEmptyNode to create a timeline object, because it initializes the new object for use in a timeline.

The IAMTimelineObj interface is a generic interface. It provides methods that are common to all types of timeline object. Each type of object exposes other interfaces as well. For example, groups expose the IAMTimelineGroup interface, among others. You can obtain pointers to the other interfaces by calling QueryInterface.

After you create an object, it is not yet a part of the timeline. The method to add an object to the timeline depends on the object type. The following section describes how to add groups, compositions, and tracks to the timeline.