Conference organizers generally pay a pretty penny to bring a seasoned key note speaker to their event. In order to help maximize that expense, we always recommend an on-camera interview be negotiated in the fee.
The on-camera interview can be a great way to summarize the theme of your conference/event, and collect key thoughts and talking points from the key note speakers presentation. This helps extend the experience.
Most of our interviews take place just before, or just after a key note speaker gives their presentation. This always us to be respectful of their time, and helps when discussing valuable parts of their presentation.