Like a certain virus we’re preoccupied with these days, Richard Wagner’s four-evening Ring des Nibelungen has a way of spinning off innumerable new variants. Francesca Zambello’s deliberately “American” staging—co-produced by the opera companies of Washington, D.C., and San Francisco—took on different shadings depending where you saw it. On the banks of the Potomac, the cycle resonated with global environmental issues. On the West Coast, the same imagery and action evoked the local history of the Gold Rush. Now, the San Francisco Opera presents a video of the 2018 revival for home viewing four weekends in March. Greer Grimsley, Iréne Theorin, Daniel Brenna, Karita Mattila, and Brandon Jovanovich head the heavy-hitting international cast. The seasoned Wagnerian Donald Runnicles conducts. For extra credit, the company has also laid on an intense schedule of festival-worthy interviews, lectures, discussions, and Q&As. —M.G.