[This is preliminary documentation and subject to change.]
Typically, the first events you add to the stream will be announcement events. Before you can transmit an announcement event, however, you must generate the file that contains the announcement data. It does not matter whether you create the announcement file before or after the enhancement stream so long as the file name used matches the one in the announcement event.
The Stream Compiler Object Library, Stream.dll, includes an object, Annc, which you can use to programmatically create announcement files. For more information, see Creating Enhancement Announcements and Enhancement Announcement Format.