What I wasn’t getting was that you specifically mean the index.html inside the Web Window object. Yes, that worked. I was also able to add a “progress” attribute to it to display the progress bar.
The one thing I still can’t do is the equivalent of the “OnDonePlaying” action in Lectora. I’m sure it is possible, but it isn’t obvious to me how without a lot of research. I can’t find any documentation in several searches on exactly what events the mediaelement.js player generates (and specifically what they’re named), and also it’s not clear to me how to have Lectora catch them. I know that’s documented somewhere.
I’m also going to have to re-encode all the video to fit on the page since the web window doesn’t like being resized, but that’s trivial.