Online video has become a daily fix for millions of people. Now entrepreneurs are starting to cash in on that obsession.

Consider Valentina Trevino. The 29-year-old Chicago artist and filmmaker regularly posts videos on YouTube, showing how she created a painting and what it means to her -- and musing quirkily on a host of matters. In one clip, she ruminates about the strange connection between the ballerinas in Edgar Degas's art and Britney Spears's custody battles.

The...