A manual demo is required as the video doesn’t state to remove a face mask before donning an oxygen mask.
Lower crewing levels often mean the demo has to be repeated, however you can usually make it work with 1 if the pax levels are low enough in certain cabins.
However this week has been a nightmare for crewing flights and trips are departing with crew levels lower than I’ve ever seen - e.g 5 on a 788 as CIHY said. In this case 2x demos would be unavoidable.