in movie terms, a definitely guaranteed, 'can't-miss' blockbuster film that promises to generate disproportionately tremendous profits due to its lucrative franchise (sequels, merchandising, spin-offs, etc.) Examples: the Star Wars franchise, the Indiana Jones films, the Spider-Man films, etc.
an excellent source of income
Is a security, investment or a project which generates or throws off lots of funds due to contacts or contracts. Sometimes, the basis for this asset is an excellent customer, a monopolistic market position, or special advantage afforded by patents, licenses, or other economic properties. This cash flow can be used for many purposes. Typically, this situation constitutes the fundamental franchise of a business.