Firex

First of all how to do an ultimate bar that when it filled up you can perform an ultimate attack
Second if so how do you make it to play a cinematic

gamingislove

Something like this would have the same setup as e.g. MP, i.e. a Normal type status value to define the maximum value and a Consumable type status value for the bar to fill.
The consumable status value increases by whatever you want to fill the bar, e.g. have the attack ability fill the bar as user changes.

Just like MP, the bar can be used as use costs for those ultimate attacks, the schematics animating the action being your 'cinematic'.