Google Blog: “…The closed captions feature is available when presenting in Google Slides. It uses your computer’s microphone to detect your spoken presentation, then transcribes—in real time—what you say as captions on the slides you’re presenting. When you begin presenting, click the “CC” button in the navigation box (or use the shortcut Ctrl + Shift + c in Chrome OS / Windows or ⌘ + Shift + c in Mac).

As you start speaking into your device’s microphone, automated captions will appear in real time at the bottom of your screen for your audience to see. The feature works for a single user presenting in U.S. English on a laptop or desktop computer, using the Chrome browser. We’re looking to expand the feature to more countries and languages over time. The captions are powered by machine learning and heavily influenced by the speaker’s accent, voice modulation, and intonation. We’re continuing to work on improving caption quality…”