Hi there, new to the forums.
Had a similar problem, for days. Tried to find a solution in forums and net, but could not. Fortunately, I have two iPad 3 (or new iPad). One worked the other did not. It drew me nuts. They are absolutely identical. The only differences were that one was 16 GB (the kids) and the other 64 (mine). The one that worked was of course the kids one. I tried everything I knew, everything but jailbraking. Even resetting and installing app by app from scratch. Nothing..... BUT, then it hit me, the kids iPad has no 3G (cellular data). The iPad were not identical. I screw av cellular data - and voila! Both iPads working as intended. Sound and video.
Hope this helps somebody else. First time I post, but I'm a regular reader and the community has helped me a lot.