Kanopy's Public Library model is Pay Per Use. Public libraries pay Kanopy $2 per play, and the transaction is triggered when a public library patron clicks 'play' and the film loads successfully. The patron has 3 days to watch the program. If the patron presses play again after 3 days, a second $2 transaction results.
Please keep in mind that most public libraries have a monthly limit on the number of plays per patron (e.g. Los Angeles Public Library only allows their patrons to eight plays per month).
(Related Article: How are Public Library Sales Reported?)