If you are getting video but no audio when using the Brainshark app on an Apple iOS (iPad, iPhone, iTouch), please check the mute function. This is to keep the iPad and iPhone from making noises during business meetings, theater, sleep, etc.
To disable the mute function, double-tap the Home button to open up the multi-task bar, flick the screen to the right. At the far left - adjacent to the iPod controls - will be the other control - i.e. this control can do either mute or orientation lock and it swaps with the physical mute switch next to the volume control.
A second suggestion is to perform a complete reboot. With the iPad switched off, press and hold the Power and Home buttons simultaneously until the white Apple logo appears. This can take quite a bit of time - about 15 seconds, but it will eventually reboot and re-initialize all the internal hardware and reset the mute option.
For the iPhone:
Put the earbuds that came with the iPhone in and click the unmute button on the right side of the earbud cord. Just click the hands-free button once and unplug the earbuds & everything should work fine.