This occurs in some browsers that have not been updated, particularly in Firefox.
You can resolve this issue by updating to the latest version of Firefox and clearing your cache. It also could be as a result of your Windows OS not supporting this media type.
This is a support article from the Firefox website
The 'No video with supported format and MIME type found' error message is about the HTML5 media player. So you do not appear to have support in Windows for playing the media file(s) in the formats that are available.
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