Configuration of the input stage application depends on two parameters in important ways. First, the pipeline source parameter is needed before a pipeline can be created, since the wcbe_src pipeline element depends on having a lag frame source. A consequence is that the input stage application cannot construct a pipeline until the WCBE_SRC_MSG message has been received. Secondly, since configuration commands are implemented in the input stage pipeline as downstream, serialized events, configuration commands cannot be acted on in the input pipeline until the pipeline is “flowing”.

Without a flowing pipeline, the application cannot handle configuration commands immediately, and instead queues configuration commands in a list of pending commands. These pending commands will be acted on, in sequence, as soon as a flowing pipeline is ready. Merely stopping the data flow with a WCBE_FLOW_MSG message will not affect any existing configurations, whereas a change of source will cause all existing configurations to be destroyed. Also, on a source change, the flow parameter will automatically be set to WCBE_FLOW_OFF. Finally, when using a file as the lag frame source, the end of file will trigger a GST_MESSAGE_EOS message on the input pipeline, which will terminate the input pipeline, thus removing the source from the input stage.