We're looking to send some serial data out from the headphone jack, but would like to still be able to play audio from the speakers. Is it possible to send output to both? If so, is it possible to send different audio to each?
Not as far as I'm aware. You can get programatic notification of when the routing has changed (i.e. when someone connects a headphone cable), but you are unable to specify which device(s) to use for output.
来源：https://stackoverflow.com/questions/10215923/ios-is-it-possible-to-send-audio-out-both-headphones-and-speakers-at-the-same-t