The Treme district is soggy under a lifeless gray sky on this chilly Sunday afternoon in February, but the sunny disposition of Kermit Ruffins refuses to be dampened.

The neighborhood's unofficial ambassador is standing in the drizzle on Treme Street while a camera crew circles him. Ruffins is one of seven locals chosen to star in a documentary about New Orleans and Mardi Gras for a French television station. The New York-based husband-and-wife filmmaking team commissioned by the French to...