InDesign would have nothing to do with what happens when you're viewing a video in your PDF reader.
What PDF reader are you using? If Acrobat or Reader, you should be asking in the Acrobat or Reader forums.
Hmm, maybe you're right, however I wondered if there was a way of putting some code onto the buttons in InDesign that would trigger the Pdf to clear Acrobats Cache?
InDesign has no way to do that. It's not something in the PDF specification. It has to do with the way the PDF reader processes the file.