Most people are ultimately making marketing videos – with the goal of selling something, whether it be a company, a product, or a service. (You might think, “Hey, there are lots of other types of videos too! The honey badgerWhat about those ridiculous honey badger videos!” Well, you’ll notice that even those that seem to be purely entertainment are selling something… in this case, he’s got his own line of honey badger t-shirts. So I would argue that many entertainment videos are marketing videos in disguise. Troll around YouTube, and you’ll be hard pressed to find a video that’s not ultimately marketing something- either a brand or a product or even a link to a site that has advertising or other products). So, for most (i.e. marketing) videos, the optimal length depends on the goal of the video itself, and where the viewer is in the sales process.