Can attendees talk in the room? Or show their webcam?
By default attendees may not talk or show their webcams as it would not be easy to manage for moderators. However, if you sign up for omNovia Web Conference Pro, you may click on an attendee name in the users list and grant them microphone or camera. If you are using the omNovia Phone conference bridge integration, you may also un-mute them on the phone.
