Authorship is now the easy part to prove, content the hard part. A signed message tells you exactly which key wrote it, so the question stops being 'is that really him' and becomes 'do I trust that key'. Video has no such handle: no signature on a frame, so every screen turns into a rumour mill. Tha...

the only way I see this could work is if Microsoft plans to become an intermediary in all the connections one makes, where everything one uploads would first go through them and in which they would modify things that one uploads