Perhaps to help compensate for a film slate that sometimes underwhelms, Tribeca thrives on its urban festiveness, surrounding its screens with musical performance, celebrity conversations, outdoor "drive-in" events, interactive exhibits and red carpets. Tribeca opens Wednesday with the premiere of Bao Nguyen's documentary about "Saturday Night Live" through the years: "Live From New York!" It's a fitting start to a theme that runs throughout the festival where a host of films peer behind comedy institutions and delve into the nature of the comedian. [...] in Kevin Pollack's "Misery Loves Company," the comic interviews stand-up colleagues on the mysterious compulsions of the comedian. The casts of "GoodFellas" and "Monty Python and the Holy Grail" will gather for back-to-back anniversary celebrations at the festival (the 25th for Scorsese's gangster film, the 40th for the cult British comedy). There are intriguing films on the controversial New York nuclear facility ("Indian Point"), police use of tasers ("Tom Swift and His Electric Rifle") and the history of sake ("The Birth of Sake"). Among the highlights is "Palio," a documentary that plunges into Italian culture — with all its passion, tradition and corruption — in depicting the centuries-old bareback horse race held twice annually in the heart of Siena. Men dot spare landscapes in a trio of indies at the festival, including Stephen Fingleton's "The Survivalist," a about a man living fearfully alone after an apocalypse, and "Mojave," a desert thriller by "The Departed" scribe William Monahan about two men (Oscar Isaac, Garrett Hedlund) who meet on the outskirts of Los Angeles.