The video tag does not recognize the source file in “Check Media”.
Here is the code example.
<video src="some_video.mp4" controls=""></video>
To avoid this, I use this hack.
<video src="some_video.mp4" controls=""></video>
<img style=""display: none;" src="some_video.mp4">
However, the Audio tag recognizes the source file, so you don’t need to do this hack.
Refence
h ttps://forums.ankiweb.net/t/video-files-are-incorrectly-listed-as-unused-files/21925