Embedded movie doesn't play in HTML5 package

Hi guys, I need to make my boss very happy and HTML5 is getting so much in the way of that. I have a movie in MP4 that plays in a full screen widget. That movie plays fine in the editor preview, the Mac package and the Win64 package, but not in the HTML5 build.
I know that one of the features HTML5 has is media playback. I assume this is not a matter of the video being corrupt or in a weird format because it plays fine in the other builds.

The video file is in the Movies folder inside the Content folder, which is where I read videos are supposed to be placed at. It’s specified in the project settings under Packaging and Specific movies to package and specific movies to copy.

Any ideas what the problem might be?

Sorry for the bump, but this is a matter of extreme importance to me. Achieving this would be the last major obstacle in making HTML5 work for our project, and I’ve spent days, including the whole weekend, watching videos, reading articles, trying and trying and more trying. It seems clear that the HTML5 implementation in UE is not the best.

Would I see the same result if I downloaded and built 4.24? I mean, I can’t find anywhere if anything changed at all regarding HTML5 in 4.24 from 4.23, but if there’s even a small chance that it will play video, I’ll go through the hassle of downloading the code, compiling and all the nice things that you need to do. But if it’s the same as 4.23, there’s no point to it.