I uploaded a bunch of files to check their mime types and .wmv was set to 'video/x-ms-asf'. It should be 'video/x-ms-wmv'.
I searched on GitHub and didn't find an open issue, so I'm reporting it here.
MIME types are determined by the underlying libraries that PHP uses, not by SMF. So this isn't something we could change.
But moreover, video/x-ms-asf isn't actually wrong. See https://stackoverflow.com/questions/53672122/why-wmv-files-have-mime-type-video-x-ms-asf-instead-of-video-x-ms-wmv.
Well SMF displays an error. "No video with supported format and MIME type found." I can play the video with Windows media player on my machine.
I had inserted the attachment in my post. I can click on the actual attachment and it will download it and play it in media player. So I guess the embed doesn't work. *shrug*
Fairly sure Firefox (and possibly Chrome?) can't integrate with the media player codecs for playing such videos like that... there's a reason most video services convert it to MP4 and other related formats, so the browsers will actually play it.
Certainly a quick search online gives me any number of suggestions for installing codecs to make it be supported, and/or services to convert it to a format they can actually play because WMV is not one of the standard online video formats. (Historically advice was to provide MP4/H.264, Ogg Theora+Vorbis, and WebM but I think MP4/H.264 won the encoding wars.)
It's pretty rare we would have somebody uploading a wmv, but if we do, I'll tell them not to embed it in a post.
Thanks for the explanation Arantor.