More info: Strangely, I copy the file and open it in VLC. Now it plays but it does not show the play position timeline (it’s always hovering at the right end of the screen) even though the time continues normally (now at over 8 minutes and counting). So is there something I can do now to reset the preview – or allow it to indicate where it is in the stream? I hope this is clear… In any case I’m much relieved to see much more of the film present than it seemed at first… So heart attack avoided, and any thoughts, much appreciated…