He's using the score which has all the parts printed down each page. I give you a link to an example. I am the musical director (MD or manic depressive) of the Tweed Coast Band and use scores during rehearsals but on the day of the gig I don't use them. I know every note and entry and if I don't then I shouldn't be out the front. However the punters seem to expect it of orchestras so most MDs use them as a prop.