You can't skim a web video like you can skim text, so the worst thing you can do is have too long of a web video.There are 3 major audiences that everyone needs to speak to, and coincidentally enough, their names tell you how long of a web video you can get away with.
1. Short Term Audiences need short videos (60-90 secs): Short term audiences are the people that know nothing or next-to-nothing about you. They want to know who you are, what you do, and if you have any value to them. You have about a minute to get that message across before they check out.
2. Medium Term Audiences are hooked, give them a little more (2-3mins): These people are into what you do, they just haven't committed yet. They want a little more detail on how you do it, who you do it for and what are your successes. They will be willing to stick around a little longer to get that information.
3. The Long Term-ers love you! (Keep it under 4-5): These are your customers and your sneezers (a Seth Godin term). They love what you do, and they want to tell others about you. You have the most freedom with this audience. If your web video is interesting, they'll stick around up to 5 or so minutes because they understand you and want to learn everything they can about you. Vlogs and general storytelling thrive with this audience.
If you still aren't sure, just keep it as short as possible. People would rather be left wanting more than boring them out of their minds.

Justin Gutwein
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