Further to Mary's suggestion of using the Lesson activity, you might provide the rationale why it is important to view the videos. The question to end the Lesson activity before moving on to the videos might be an agreement which the students would click, acknowledging their adherence to the agreement before moving forward to the videos. This would add a formal pause, rather than only presenting a button to move forward.
In the end, there isn't really a way to enforce adherence in an unsupervised environment. You will want to appeal to the students' honesty and academic integrity.
In the end, there isn't really a way to enforce adherence in an unsupervised environment. You will want to appeal to the students' honesty and academic integrity.