iphone 7 plus 4k playback too slow

Hi,

All my iPhone 7 plus 4k video recordings are playing in slow motion (Lag) on my 70 inch 4k LED TV. I have an amlogic s905 based player which plays all the iPhone 6s plus recorded videos just fine. I also tried to play a iPhone 7 plus 4k video taken from a friend's phone and still slow laggy playback.

I looked up the video specs on apple.com for iPhone 6s plus and iPhone 7 plus and both seem to be same.

Can someone throw light on whats going on?

Thanks,