"You Ain't Seen Nothing Yet" is a love letter to the acting profession that shows a troupe of thespians performing a play based on the Greek myth of lovers Orpheus and Eurydice.
There are several plays-within-a-play in the drama, which features a who's who of French dramatic talent, including Lambert Wilson, Michel Piccoli and Mathieu Amalric.
The 89-year-old Resnais says he was trying to show the similarities between theater and film, often portrayed as very different.
He said Monday that "people often say that the theater is a noble art whereas films are not."
But, he said, "in both cases, you need actors."
The festival runs until Sunday.