Make a button and apply action to it (Video, play, stop) from Button and Form panel
Unfortunately it is a function of Acrobat that sets the movie to play when clicked. However, there is a workaround.
Place your video in ID. Set a button to play it.
Create a new object with Fill: None, Stroke: None, bigger than the video frame. Make this a button with no actions.
Now, this object will block the video from being able to be clicked. But a "hand" icon will appear when the user hovers over the button. So in the description for the button put something like "Click the button to play the video."
I can't do any better than that.
Great idea, has solved the problem - thanks very much for your help!