Transfers the buffered output events to sequencer. Function returns zero if successful, or a negative error code. If the output memory pool of the current client on kernel space becomes full during flush, the function falls into sleep in blocking mode, or returns -EAGAIN error in non-blocking mode. If an error occurs, the transfer stops at the error event. The error even still remains on buffer. In order to remove such an error event, use snd_seq_extract_output.