Stream Control

Microsoft DirectShow 9.0

Stream Control

The IVMRVideoStreamControl interface on the VMR's input pin(s) enables applications and upstream filters to control the behavior of the mixer component, including the Z-order and the active state of the VMR's input streams. Although this interface is exposed on the pins, it operates on the VMR's mixer component, so it is only available when the mixer is loaded, which is when the VMR is processing multiple input streams. Upstream filters use the SetColorKey and GetColorKey methods to control the source color key. These methods enable effects such as the overlay of animation over video. Simply set the color key to the animation stream's background color, and the VMR will mix that stream with another video stream. Applications should take care not to change the color key to some value that is different than the value being used by an upstream filter, such as a decoder.

Filters use the GetStreamActiveState and SetStreamActiveState methods to tell the mixer whether to expect input data from a specified pin. For example, the Line21 Decoder uses these methods to activate the VMR's input pin for Line21 data only when that data is present in the stream. Setting a pin to an inactive state instructs the mixer not to wait for data from a specified pin before compositing the image.