black screen loading mp4 on andriod (storyline2)

hi having a video loading problem with an mp4 video when puplishing the lms in storyline 2. shows black screen on loading on andriod rather than the first frame of video  which Id prefer. It works fine on pc and ipad. Have tryed the QTindex for making video progressive and is front loading so that isnt the problem. was reading sometimes mp4's have black frame at beginning not sure if it's loading on that frame? video was rendered in adobe media encoder as H.264

anyway any ideas be appreciated, jack