Some system-level messages, such as WM_PALETTECHANGED and WM_QUERYNEWPALETTE, are sent only to top-level and overlapped windows. If a capture window is a child window, its parent must forward these messages.
Similarly, if the parent window changes size, it might need to send notification messages to the capture window. Conversely, if the dimensions of the captured video change, the capture window might need to send notification messages to the parent window. The simplest way to manage this is to always keep the capture window dimensions equal to the size of the captured video stream, notifying the parent whenever these dimensions change.