The shoot keys emulation does not work also for sx420 and ixus180.
_PostLogicalEventToUI(4484, 0);
levent_post_to_ui_by_name("PressRecButton");
msleep(400);
levent_post_to_ui_by_name("UnpressRecButton");
not work too.
As last resort, try the following levents:
PressSwOne, UnpressSwOne (this is shoot half)
PressSwTwo, UnpressSwTwo (this is full shoot)