FCEUX support sockets, there must be
some docs. Write an app that would generate sockets and send them to fceuxes. Background input would not need to be enabled I believe.
Quoting IRC so nothing gets lost:
feos: your app would need fceux instances to report success of the last action, and then you would say "Ready" to prompt for new actions
feos: or it just won't accept anything before all instances return success
feos: "Add emulators" does not look necessary
feos: meshuggahTAS: virtual controller might as well poll and return the movie state as an uneditable listvew. say, active frame in the middle, 5 future frames with controller state below, 5 past frames with controller state above.
feos: and yeah, you would need to plug controller to your app as emulators allow. so that you could press A+W and Left+Up presses get registered
feos: press keys, hit frameadvance. everyone is happy
feos: virtualpad would visualize which buttons are pressed with input keys