The MCI_OPEN message is issued to create a device context of the digital video device. A default window is created and displayed when the device is opened if the device is cued for output or a movie is loaded. The video device directs its output to the default window. If a window is specified with the MCI_WINDOW message the video device directs its output to the window specified. For the convenience of applications that are using the string interface, some window-style control functions are also exported as flags to the MCI_WINDOW message.
Whether the default window or an application-defined window is used for output, the digital video device confines its output to the device coordinates of the specified window.
The default video window is invisible when the device is first opened. This allows the user or application to prepare the size, position, and contents of the window before it is displayed. It is created in a frame window, which can be sized, moved, maximized, and minimized. It is also created with an ideal aspect ratio in the center of the display and occupies approximately one quarter of the screen. As the user changes the size of the window, the digital video device scales the video image as required to maintain the video within the current coordinates. Maintaining a constant aspect ratio is the responsibility of the application program.
The parent of the default video window is HWND_DESKTOP unless otherwise specified in the MCI_OPEN message. The owner of the default video window is NULL. An application can specify a parent window handle for the default video window using hwndParent when the device is opened. This is the only window-related parameter that can be specified using media control interface commands that changes the behavior of the default video window.