Hello. What I would like to do is add an icon (or just a tiny picture, but one of my own choosing) to a slide such that when it's clicked on (or double-clicked, if need be), a separate floating window opens up in which an MP4 video appears. Can this be done?

Have you tried this?

- Insert >> Object >> Create from file >> Browse >> select your video file
- Insert the picture you want to click on to play the movie
- Select your movie object on the slide >> go to Animations tab >> Add Animation >> OLE Action Verbs >> Activate Contents
- Open the animation pane
- Select your movie object in the animation pane >> in the Animations tab go to Trigger >> On click of >> select your picture

Thanks, but I did not manage to follow those instructions, probably because of my addled brain. However, I did find a way to insert an icon that plays a movie: simply put the icon on the page by Insert > Picture (and browse to the desired picture). Then right-click and insert a link to the URL of the movie (in my case, an MP4 file on one of my folders).
By the same approach, I was able to insert an icon that opens an audio clip. But there was a wrinkle: Doing Ctrl-Click on the movie icon simply opens it without delay, but Ctrl-Click on the audio icon leads to an irritating warning message first. This happens both for WAV files and for MP3 files. (I'll put this last part in a separate post so everyone can see it.)