Run method notifies the pin that the filter is now running.
Start time as passed to the filter's IMediaFilter::Run method.
When the filter goes from paused to running, the CBaseFilter class calls this method on all of the filter's pins.
This method does nothing in the base class. Derived classes can override this method. For example, a pin might start a worker thread that delivers samples.
The filter graph manager's internal state is not updated until after this member function returns, so do not test the state from this method.