Fig. 1. Fighting for his life - part of a corporate training series aimed at the emergency services and utility companies to create greater understanding of the need to report incidents as they occur.
Some times 10 seconds is too long for a video - while ten hours doesn't even start to do justice to the speaker or theme.
I wouldn't give extreme views the time of day, on the other hand, I would listen to everything Mandela had to say for hours. Horses for courses.
Stats lie - they certainly require interpretation.
Is a minute or ten minutes of video too much or too little? When do people turn off or tune in to a piece of AV, whether a movie, TV show, video or slide show mocked-up in PowerPoint? 'Death by PowerPoint start for me in this first second.
Research from the Open University shows that people decide whether to continue watching a piece of video in under 35 seconds. This is not the same as a 45 minute lecture from an expert that is required as part of a formal course - though there should always be a transcript. Personally I work between the two and replay if there is something important.
Who needs the research? You can tell intuitively if what you are about to see is of interest or not?
My 35 seconds video? A party balloon is blown up by someone with breathing difficulties. The words on the balloon gradually appear - 'The Cost of Asthma' - the professionally composed and performed music tugs at the heart strings and a professional broadcaster says some pithy words.
My 35 hour video?
Interviews with some if the greatest thinkers alive in the planet today. Vitally, especially online, as producers we offer what is a smorgasbord - the viewer decides what to put in their plate and whether to eat it - and whether to stuff it down or take it in bite-sized pieces.
You had might was well ask 'how many pages should there be in a book?' or 'how many posts in a blog?' It depends on many things: context, budget, goal, resources, subject matter, audience, platform, shelf-life ...