Dear Opera Companies,
When you're making up preview videos for popular newbie operas, don't put major plot spoilers in the first ten seconds of the film. I'm just guessing that the filmmaker isn't an opera fan and didn't bother to ask anyone, but didn't somebody inside the company approve the preview before you posted it?
When I take friends to that particular opera and it's their first time seeing it, I tell them not to read the synopsis. Some surprises you can only have once.