What should be inserted at the end of a lengthy audio or video presentation to indicate its conclusion?

Inserting a concluding parenthetical at the end of a lengthy audio or video presentation serves as a concise signal to the audience that the presentation is complete. This notation effectively encapsulates the presentation's end, making it clear to the listeners or viewers that they have reached the conclusion. It provides a formal closure, often seen in professional documentation and transcriptions, reinforcing the finality of the content.

While summarizing key points might provide value, it is typically used to reinforce the message during or after the presentation rather than serve as a definitive conclusion. Similarly, listing speakers may offer context or recognition but does not indicate the conclusion of the material. A brief introduction would serve to initiate the content rather than signal its conclusion, making it ineffective in this context. Therefore, the concluding parenthetical stands out as the most appropriate choice to denote the end of the presentation effectively.