Indeed this shows the footage a few crucial seconds earlier than other videos I'd seen. It seems to have both the moment of touchdown of JL516 as well as looks to show JA722A coming to a stop on the runway and standing for >30 seconds before impact.

I wonder if the JCG crew thought they were cleared on to 34R via C5 to hold, (rather than hold short of the runway at C5) and were waiting for clearance to takeoff while sat there, while not realising the runway was in use for an active landing, and sadly ATC also didn't notice the incursion (at least in time to warn JL516 to go around).