Place it at the very end of the helpful moment, once the favour is clear on screen, then follow it with a short burst of applause to close the scene on a warm note.
关于此声音
This short clip is a clear, polite spoken phrase, 'thank you, sir,' delivered in a warm, respectful tone over about three seconds. It feels sincere and slightly formal, with a touch of old-fashioned courtesy that makes gratitude sound deliberate rather than throwaway. It works as a quick, good-natured thank-you that lands without needing any extra explanation.