Classix movies & TV shows play using the standard Apple video player, because of this it follows the device limitation of the ringer switch on the top left side of the device needs to be on.
Most likely your device is set to vibrate. Flip the switch on the top left side of the device towards you and you should have sound.
On iPads without a side switch both Rotation Lock and Notification Mute are controlled via Control Centre (swipe up from the bottom edge of the iPad) - they are the two icons on the right of the top row of icons. Also ensure your iPad is not in airplane.