Is the subscription flexible like that or does it just gate 100% of videos behind the subscription?
That really depends on you develop your channel. For instance, I have a channel that offers free and sub content. The app checks with Roku for a valid subscription before loading the assets, and depending on the result, offers either free or paid content to the viewer. It's not really Roku who decides what content is available, that is for your app or back-end to manage.
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