So...
Seeing as I am clearly a bit thick here.
I can get videoPlayer to work, I just can't hide the controls and I need to do that.
I found this other video player extension, but just cannot get the path correct.
What would be the required path to access the Vid1.mp4 video that I have uploaded to the editor?
I know where it is on the phone .....(\Internal storage\Android\data\edu.mit.appinventor.aicompanion3\files\assets\Vid1.mp4)
But that fails for reasons I think you have already pointed out.
I didn't think this was going to be so annoyingly difficult (for an idiot like me)