For IOS, please use only mp4 source file. I have observed one issue in latest safari browser that safari browser cant able to detect source file correctly and because of this, video autoplay doesn't work.
Lets check below example -
<video autoplay loop muted playsinline poster="video_thumbnail/thumbanil.jpg" src="video/video.mp4">
<source src="video/video.mp4" type="video/mp4"></source>
<source src="video/video.webm" type="video/webm"></source>
</video>
As I have used mp4, webm in source files. Safari deosnt support webm but still in latest safari version, it would select webm and it fails video autoplay.
So to work autoplay across supported browser, I would suggest to check browser first and based on that you should generate your html.
So for safari, use below html.
<video autoplay loop muted playsinline poster="video_thumbnail/thumbanil.jpg" src="video/video.mp4">
<source src="video/video.mp4" type="video/mp4"></source>
</video>
For other than safari,
<video autoplay loop muted playsinline poster="video_thumbnail/thumbanil.jpg" src="video/video.mp4">
<source src="video/video.webm" type="video/webm"></source>
<source src="video/video.mp4" type="video/mp4"></source>
</video>