What Is the Ideal Length Of An Online Video Ad?

Conventional wisdom says that the perfect film is two hours long and that the perfect pop song is three minutes long, but how long is the perfect online advert?

We encounter video adverts online on a daily basis. Some are promoted on Twitter, others appear in banner ads and others are spread directly across social media platforms or ‘dark social’ like email and IM. And with a spot’s ‘viewability’ (i.e. its ability to not only gain but retain a viewer’s active attention) set to become the industry marker for 2015, you have to wonder: what length of ad is most likely to engage viewers?

Ask pretty much anyone if attention spans are decreasing and they’ll say “yes”, before tuning out to check their newsfeed. Every day we’re told that the 21st Century cocktail of 24 hour news, clickbait ‘listicles’ and smartphone games have left us hopefully impatient, picking up and dropping stories the second we’re bored. Goldfish with 4G, essentially. But is this actually true?