In addition to
webView.allowsInlineMediaPlayback = true
Your video must have the webkit-playinginline attribute.
Below is the text from Apple docs:
"In order for a video to play inline, you must not only set this property in the view, but the video element in the HTML document must also include the webkit-playinginline attribute."
So, your video tag should look something like this: <video class = "poster =" "webkit-playinginline>
Since you want to play vimeo, you will need to see if it is possible to add this attribute, otherwise it seems impossible.
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