This dialog configures the way the exported frames are written to file. The default is designed to be compatible with the tcpflow file naming scheme, except that it is bidirectional:

The placeholders can be used in any of the input fields. Special fields are the count field that is increased for each new file, and the filterlabel field that takes the filter label specified in the flow filters table. The main use for this is to be able to put the snort signature name into the file name or path.