iPad has no sound when playing back videos

When you were recording the video, was your finger or any thing over the mic? There are two mics on the iPad, above the front camera, hard to see if you have a black iPad, and one further ahead, with a small hole. It could be that, or any liquid that touched the iPad could of interfered. It could be those things, or, a technical problem inside the iPad itself when recording the videos. If I were you, I would take it to the Apple Store. (Tip: If you have a jail broken one, restore it so Apple can help you. They would most likely refuse if it is jail broken.)