Why does html5 work weird in macOS/iOS safari?

Question

HTML

<video preload="auto" playsinline webkit-playsinline poster="/poster.jpg" id="video">
<source src="video.ogv" type='video/ogg; codecs="theora, vorbis"'>
<source src="video.mp4" type='video/mp4; codecs="avc1.42E01E, mp4a.40.2"'>
<source src="video.webm type='video/webm; codecs="vp8, vorbis"'>
</video>

When you open a page in Safari from any apple device and press play, the video freezes for a few seconds (5-20) and only then playback starts. At this time, the problem is not observed in other browsers.

Another thing I noticed is that there is a pop-up window on the page, it has a "close" cross button, cross - svg inline element, and so it is not displayed until the video starts playing.