Marketers cannot cede their storytelling to Facebook, but they do need to listen to Facebook’s feedback based on analysis of engagement with video. There’s no one magic formulae or video length, just the right combinations of medium, story, and time, which will vary based on the novelty of the story, the challenges to existing narratives (“I just don’t do things like that,” for example, in response to a new product — think of your parents’ reaction to Snapchat.)

Facebook will have a notion of what kind of video fits on Facebook. That doesn’t mean marketers should always follow that advice blindly. It’s just one more input in the creative and strategic decision process.

Facebook has had big goals for video for a while and advertisers are ramping up the amount of video content that they produce for the platform. However, brands are still pouring hefty budgets into producing TV assets that don’t necessarily work on mobile where consumers are increasingly watching more video.

Source: Facebook Wants to Help Brands Tailor Their TV Ads for Mobile – Adweek