A common topic is how long should a video be? Sure, the complexity of the topic will have an effect. I recently took a MOOC via Coursera about Hybrid instruction. Some of the learning objects were short videos on teaching tips from Renton Technical College. Here is a link to the playlist. I felt that the effective videos were 5 minutes or less. They got to the point and they didn’t stray off topic. In short, they didn’t waste my time and get too cute.
Those who use Lynda.com we be familar with the same idea. Their videos are broken up into specific topics. In instructional terms, the videos are “chunked” into distinct topics.
I don’t think there is a magic number for the length of a video object, but we should all be familliar with how our attention wanes as time goes on.
This is a chart from Wistia.com. They did a study of their own hosted videos and found a negative correlation between length and engagement. We shouldn’t be surprised at the result.
The biggest drop is after 20 minutes, but overall, engagement steadily goes down over time. Is your 45-minute lecture or interview actually 9 separate 5-minute segments? Are you using titles or superimposed text to help the viewer understand the content? I think the lesson is that the longer your video is, the more you have to pay attention to quality. You can’t have some fluff after 10 minutes or you’ll lose your audience quicker.