“About as long as Parsifal and not as funny,” Noël Coward said of Camelot. What might he have thought of Chausson’s swirling Wagnerian tragedy on the same subject, Le Roi Arthus? For the record, Chausson’s opera is way shorter than Parsifal; as for funny, there are no jokes of any kind. At its best, the score is oceanic, with Arthur, Guinevere, and Lancelot swimming valiantly against the flood tides of their tangled destinies. Watch, too, for Mordred and Merlin machinating at the fringes of the action. Norman Garrett has the title role, opposite the luminous Sasha Cooke as the queen. The talented Louisa Proske, who is popping up everywhere these days, directs. Leon Botstein, who gave the score a triumphant concert premiere at Lincoln Center several seasons back, descends into the pit, where an opera conductor belongs. Live streaming links available at $10 for real-time viewing only. —M.G.