I'd not recommend running a projector on UPS alone as I'm pretty sure that it won't be drawing the same current all the time - And to get something close to running a unit (other than a feasibility test) for any useable length of time will require bulky and expensive batteries.
Have you considered using a surge protected jenny instead?
In science one tries to tell people, in such a way as to be understood by everyone, something that no one ever knew before. But in poetry, it's the exact opposite - Paul Dirac