VMR Windowless Mode

This topic applies to Windows XP Home Edition and Windows XP Professional only.

Windowless mode is a new feature of the VMR and it is anticipated that this mode will become the preferred way for applications to host video playback within their own application window. In windowless mode the VMR unloads its window manager and therefore does not support the IBasicVideo or IVideoWindow interfaces. Instead, the application provides the playback window and uses the VMR's IVMRWindowlessControl interface to specify a destination rectangle in the application window's client area. In windowless mode the VMR creates and configures a DirectDraw clipper object to ensure that the video rectangle is correctly clipped to the application's window and does not appear on any other windows used by other applications. The VMR does not subclass the application's window or install any system/process hooks.

Windowless mode is supported for single input streams and also for multiple streams using the mixer and compositor. In windowless mode, the sequence of events during connection and transition to the run state is as follows:

• The upstream filter, typically a decoder, proposes a media type and the VMR determines whether to accept or reject it.
• If the media type is accepted, the VMR calls the Allocator-Presenter to obtain a DirectDraw surface. If the surface is created successfully, the pins connect and the VMR is now ready to transition into the run state.
• When the filter graph is run, the decoder calls GetBuffer on the allocator, and the VMR queries the Allocator-Presenter to ensure that the pixel depth, rectangle size, and other parameters on its DirectDraw surface are compatible with the incoming video. If they are compatible, then it returns the DirectDraw surface to the decoder. After the decoder has decoded into the surface, the VMR calls Receive on the Core Synchronization Unit, which performs a sanity check on the time stamps , and then IReferenceClock::AdviseTime is called. The Sync Unit blocks the Receive call until the presentation time arrives. At that point it calls Present() on the Allocator-Presenter , which “presents” the surface to the graphics card.

The following illustration shows the VMR in windowless mode with multiple input streams.