Live Captioning
real-time live captions of the speech during a presentation
September 22, 2025
Samantha Monty
Chair for Human-Computer Interaction, University of Würzburg

What is Live captioning



  • Enable real-time live captions of their speech during a presentation.
  • Broadcast those captions to the audience, either projected or sent to their devices via a QR code.
  • Configure the system with specific language settings and a caption server.

How we can enable it ?

  • Start presenter mode by pressing P three times in quick succession.
  • A Button should be visible in the top right.
  • Click it, be aware of the warning and a popup with a black page should open. Keep it open. You may reposition the popup onto a projection space for your whole audience to see.
  • If a caption-server is supplied then a QR-Code will be displayed for your audience to scan.
  • Attendees with hearing problems can read your live captioned voice on their mobile device.
  • Closing the black window also ends captioning.
  • Clicking the button again, now displayed as , re-displays the QR-Code and allows you to stop the captioning.

Deck Configuration

You should add this configs into Deck at the start of your markdown file

Source code :

live-captions: true
caption-server: https://decker.cs.tu-dortmund.de/captions
speech-recognition-language: de-DE
  • live-captions: true : Enable the feature in the default template.
  • caption-server : An address to a running live-captioning sync service.
  • speech-recognition-language : If not supplied, the WebSpeechAPI uses your browser’s default language. If supplied it takes a BCP 47 language tag.

Language Tag Parsing

As a common user might now be versed in these language codes, the following is also allowed:

  • A 2-letter language code
  • A 3-letter language code of “deu” or “eng”
  • A BCP 47 5-letter language code that matches the RegEx “/^..-../” (two two-letter codes separated by a dash)
  • The phrases “Deutsch”, “German”, “Englisch” or “English”