Prevent video stutter / lag in h264 on iPad
From the look of the specs page, the current iPad (4) can handle up to 2.5Mbps MPEG 4 video at HD resolution (1920x1080) at 30fps. 

Going above this will result in what you described. See discussion link below:

https://discussions.apple.com/thread/5012754?start=0&amp;tstart=0