Cannot rotate video in video app of iOS 8.4

When i transfer a video( with heigh: 720 > width: 406 ) from itunes to my iphone then open it in default video app of iOS 8.4 in my iphone, it's cannot be rotate to fill to the blank at the both side look like picture below 😟 How to fix it ? i use iphone 5s and ios 8.4