Unlike some media applications, Azoomee will not play audio if you put your device on silent. If you are not able to hear any sound please make sure you un-mute your device and turn the volume up.
All iPhones and most iPads have a silent/ringer switch on the side of the device. Make sure this is not set to silent, then press the volume up button.
If you have a newer iPad, the mute switch is accessed in the Control Centre by swiping down from the top-right of the screen.