What you’re looking for is playsinline
which can be added to any video
element. This works beautifully on inline videos on iOS 10.
The Webflow team might want to add playsinline
to their default background video element, considering users would have to manually inject using JS as a workaround until then. 
<video
autoplay="autoplay"
playsinline
loop="loop"
style="width:100%"
"background-image: url(POSTER-URL)">
<source src="WEBM-URL">
<source src="MP4URL">
</video>
To demonstrate, open this link from an iOS 10 device to see the video element autoplay:
http://playsinline.webflow.io
Here’s the Webflow project:
https://preview.webflow.com/preview/playsinline?preview=d7203661bd3a954f957f464a6b46c623
Note: playsinline
will not work if your video has an audio track. If you’re unable to remove the audio track from a video, you can add muted
to the video element.
<video
autoplay="autoplay"
playsinline
muted
loop="loop"
etc...