This method is part of a family of three methods which force buffered bytes to be moved to the underlying Sink . Calls to this method cause all buffered bytes to be moved to the underlying Sink and then that Sink is also instructed to flush itself. When the video is done encoding and no more bytes will be written a call to emit() (with the same caveats as the last paragraph) or flush() should happen so that the final bytes are not left in the buffer.