I can't use the first fram of the video to be thumbnail in mobile

I use Video.js Plugin, When I preview with a PC it’s show the first frame of the Video to be the thumbnail. However, it won’t show in the mobile (I use Iphone). I try to check the autoplay checkbox, it’s work but when I navigate the page (to the same page) it will show up the video in fullscreen and that’s a problem too. I just don’t want to autoplay it in first place. I also try using the video : to be parentgroup’s video#t=0.1 still don’t. now I have no idea. Please someone help!

Cauz it is different OS platform.
I assume iOS doesn’t support to capture first frame.