Reconnecting Pins

During a pin connection, a filter might need to disconnect and reconnect one of its other pins. For example:

• Suppose that a filter's input pin is already connected with a certain media type. When the output pin attempts to connect, it might be unable to find a media type compatible with the input type. To complete the downstream connection, the filter must reconnect the input pin, using another type.
• To reduce copying, some transform filters modify data in place. (See the CTransInPlaceFilter base class for an example.) The filter does not provide its own allocator. When the output pin connects, the filter reconnects the input pin and offers the downstream filter's allocator to the upstream filter. In this way, all three filters can share one allocator, minimizing the total buffer requirements.

To reconnect, the filter calls IFilterGraph::Reconnect or IFilterGraph2::ReconnectEx on the Filter Graph Manager. The Filter Graph Manager asynchronously disconnects and reconnects the pins. The ReconnectEx method is preferable, because it specifies a media type. Otherwise, the filter that initiates the reconnection must store the intended media type internally.

The filter must not attempt a reconnection unless the new connection is guaranteed to succeed. Otherwise, the pin will be left disconnected, causing graph errors. If the filter reconnects with a new media type, it must specify a media type known to be valid. If in doubt, call the IPin::QueryAccept method.

Also, the filter should request the reconnection from inside the IPin::Connect method, on the same thread. If the IPin::Connect method returns on one thread, while another thread makes the reconnection request, the Filter Graph Manager might run the graph before it makes the reconnection, causing graph errors.