Why can't I import an MP4 Video into Music?

The procedure for importing music or videos into the Music app is well known to me. I have done it many times with no fuss. For some reason now, I cannot import an MP4 video into the Music app.

I have tried File > Import from the Music app. I've dragged the file into the Music app. I have manually placed the video in the location where the Music app stores them. I can see all of my videos there, including video I moved in the Music app folder. The video I'm trying to move simply does not show up in the music app. When I search for it by name, I get no results. When I look under Recents, it is not there.

My video is about 3 minutes long. It plays perfectly with QuickTime, and several other video playing apps.