Your idea reminds me of an episode on either Dragon's Den or Shark Tank (the American version), where 2 college entrepreneurs just like you created a business to have students sign up and exchange or purchase quality notes from fellow students. They divided into Colleges, and then courses. The idea is study notes from top students are really useful, and college students skip classes a lot (you know it!) and they need a way to make it up.
I think the video idea might work. Many professors allow you to video tape it, just take a look at Yale University's open courses, video taped through the semester and made available to everyone
pro: niche market, there are quite some firms in the notes and assignment help arena, the video thing is refreshing
con: more difficult to get the materials, but materials will have higher quality, also its more complicated to host videos than buying notes
Hope that helps
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