Handling Termination

Microsoft DirectShow 9.0

Handling Termination

Video renderers must correctly handle termination events from the user. This implies correctly hiding the window and knowing what to do if a window is subsequently forced to be displayed. Also, video renderers must notify the Filter Graph Manager when its window is destroyed (or more accurately, when the renderer is removed from the filter graph) to free resources.

If the user closes the video window (for instance by pressing ALT+F4), the convention is to hide the window immediately and send an EC_USERABORT notification to the Filter Graph Manager. This notification is passed through to the application, which will stop the graph playing. After sending EC_USERABORT, a video renderer should reject any additional samples delivered to it.

The graph-stopped flag should be left on by the renderer until it is subsequently stopped, at which point it should be reset so that an application can override the user action and continue playing the graph if it desires. If ALT+F4 is pressed while the video is running, the window will be hidden and all further samples delivered will be rejected. If the window is subsequently shown (perhaps through IVideoWindow::put_Visible), then no EC_REPAINT notifications should be generated.

The video renderer should also send the EC_WINDOW_DESTROYED notification to the filter graph when the video renderer is terminating. In fact, it is best to handle this when the renderer's IBaseFilter::JoinFilterGraph method is called with a null parameter (indicating that the renderer is about to be removed from the filter graph), rather than waiting until the actual video window is destroyed. Sending this notification enables the plug-in distributor in the Filter Graph Manager to pass on resources that depend on window focus to other filters (such as audio devices).