HRESULT 0x80040204 (VFW_E_ALREADY_CONNECTED): meaning and diagnosis

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Description:

At least one pin involved in the requested DirectShow connection is already connected.

Could be also:
Constant	Type	OS
EVENT_E_QUERYFIELD	HRESULT	Windows

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EVENT_E_QUERYFIELD	EVENT_E_INTERNALEXCEPTION

VFW_E_ALREADY_CONNECTED

VFW_E_ALREADY_CONNECTED is a DirectShow HRESULT. DirectShow pins normally have one peer connection. This result means that the application is trying to connect a pin that is already bound into the filter graph, often while rebuilding or replacing a portion of the graph.

What to check

Use IPin::ConnectedTo to inspect the current peer before requesting another connection.
Disconnect both ends through the graph manager when a connection really must be replaced.
Perform topology changes while the graph is stopped so filters can release the current connection cleanly.

If automatic graph building created the existing connection, remove or reconnect the affected filters through the same graph manager instead of connecting one pin directly.

Microsoft: DirectShow filters and pins

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