That's the 1973 video of the Glyndebourne stage production directed by Sir Peter Hall (a GREAT opera director in addition to all his fine Shakespearean credits). It's my own first choice, with Te Kanawa, Ileana Cotrubas, and Frederica von Stade in the summer when she burst upon Europe (after a season or two singing small roles at the Met) and enchanted everyone.

There's also a film directed by Ponnelle; that may be the 1976 one you mention. I find it not as successful: poorly lip-synced or else sung in voice-over (which to my mind never works in opera) though there are some intriguing casting elements.