A video that goes viral is usually one that has at least 10,000+ views on YouTube, about 1000+ shares in a 24-hour period, has repeating interest of the viewer, has content that inspires "unaided" sharing, and of course a potentially wide bandwidth of audience interest. And they're usually short (Kony 2012 being an exception).
A video that one hopes will go viral is solid on content to start with. The concept has to be instantly attention grabbing, fresh, relevant. With today's trend becoming yesterday's "404 Page Not Found" in this ever changing digital savvy world, one needs to focus hard on being up to date. You can keep track of what's hot, what's not by checking out the trend charts on this site. And you can watch some of the top ones from 2011 here.
Most videos that go viral are short. The first 30 seconds are crucial. It's like a tv spot. The attention has to be grabbed in 30. Short, sweet, shareable. Brands that come to agency with "viral video" briefs need to realize that content needs to be less on brand and more on emotion and relevance. With a video intended to go viral, it's important to use the right title, easy and memorable keywords, and of course a blockbuster thumbnail.
From a brand standpoint, working closely with the agency (both content and media), towards driving the sharing momentum is key. Optimizing the video for sharing is a good starting point, but beyond that it's identifying the first batch of targets (either accidental and hopeful or planned and orchestrated). It's important to define channels of first contact – these should be relevant to both the topic and to the target audience. Tweets and re-tweets, blog posts, email sharing and facebook wall posting all work better in the early stages than say, a "watch our video" tagline at the bottom of a print ad i a magazine or outdoor.
If you look at some of the videos that went massively viral, there are some unique hallmarks that stand out. The title of the video is important – short, interesting, attention grabbing. So is the thumbnail. The thumbnail isn't the first frame of the video – it should be the single most attention grabbing, share inspiring single frame from the video. And, in many cases, it depends on the "viral sneezer" – the viewers who propagate the sharing – trusted friends, celebrities, news channels covering it, etc. There is a herd mentality in every successful "viral video" that's notched up the charts. Viewers like to watch (and share) what many, many others are watching.