A simple WebM video with the autoplay attribute set does not seem to play correctly in Safari 15.3:

<video autoplay muted playsinline controls>
 <source src="https://www.homepage-helden.de/cms/test.webm" type="video/webm">
<source src="https://www.homepage-helden.de/cms/V/startloop/Homepage-Helden-Hamburg-2019-S_low.mp4?v2022-2" type="video/webm">
</video>

The video starts playing then freezes. When the playhead reaches the end it starts playing again. I noticed that when switching tabs the video unfreezes too.

It does not make difference if the WebM Video is encoded with the V8 or V9 Codec. CanIuse claims that Safari 15. support WebM videos in Version 15 since MacOS 11.3

When Safari in Verion 15 is given the choise between an MP4 and a WemM file it chooses to play the WebM file and fails.

Here is a video: https://filebin.net/l77ctp61v8gtje7t

Is this a known safari bug? Or has it something to do with the encoding? Or with HTTP Headers?