Have you tried Adobe Reader on the iPad?
That should play it just fine.
Did you move to iOS7? If so, could be related to that...or not.
Interactive PDF on iPad, or any mobile device is a crapshoot at best.
Video is NOT supported on Adobe Reader for iOS or Android. Your best bet is PDF Expert. There may be others, but you'll have to look around (and don't look for a free one).
I tried expert pdf and all was well. In fact the mp3s work better too, with proper controls. It does seem to be a bit hit and miss with media... Can't understand why adobe reader doesn't support media properly.