Having recently become involved in Television production, there's also privacy laws and informed consent to take into consideration if the video or audio are going to be distributed in any way (even on DVD from you, even if only to WSFS members present). I'm positive Japan has different laws than the U.S. too.

It's often considered enough in the U.S. to say (and have posted for latecomers) approximately "we're recording - if you don't want to be recorded leave now." Though that may not be the case in all jurisdictions, and it's not really been tested.

It's a wrinkle to consider, if nothing else.