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Live source: the phone streams into the slide

liveForTeaching staff

A phone's camera, screen, photo or video appears live on the slide — with sound, directly from device to device, without recording. Paired via QR code, accepted by the presenter.

Why#

An experiment on the lab bench, a sketch on paper, a guest in the room, a video from the phone: instead of holding the phone under a camera or sending files back and forth, its image appears exactly in the spot the slide provides for it — and can be pulled across the whole slide on request.

How it works#

Click pathCourseContentSlidesEdit largeInsertLive source (phone)

  1. 1In the slide editor under “Insert” → “Media” → “Live source (phone)” open the panel and choose “Insert live source”.
  2. 2Move and scale the spot like any element; in the panel set aspect ratio (free, 16:9, 4:3, 1:1, 9:16, 3:4), show image whole or fill, corners, border, background, label of the placeholder, sound, volume and mirroring.
  3. 3Presenting: in the presenter view, below the lever console, is the console “Live sources” — “Pair phone” shows a QR code (only there, not on the projector). Without a presenter view: “Live sources” at the bottom left of the presentation.
  4. 4On the phone scan the QR code, confirm the data protection notice, choose the source (camera rear/front, screen, photo or video, sound only), microphone on or off, “Request to send”.
  5. 5The presenter sees “… would like to send live” — “Accept” or “Decline”. Only after accepting does an image go out.
  6. 6Live: sound on/off, volume, mirror, “Full screen” (the source covers the slide), “Back to slide”, “Disconnect”. The same by voice and with camera gestures. On the phone the source can be changed at any time without pairing again.
  7. 7In the editor the same pairing works as a preview (without sound) — in the panel “Live source” under the settings of the selected spot.

Settings and switches#

  • Switchable per tenantDefault: onModule: Kurs-Studio
  • Switchable per tenant (feature “Phone stream in slides”, default on). Off: live sources only show their placeholder, the panel is missing in the editor, the phone page does not respond.
  • Part of the module “Course Studio”.
  • For connections across firewalls the operation needs a relay server (TURN, environment `STREAM_TURN_URLS` and `STREAM_TURN_SECRET`). Without it, it works reliably on the same Wi-Fi, but not always via mobile networks and strict networks — the interface then says so.

How the connection is made#

The QR code contains a random, short-lived room code. The phone registers in this room and makes a request; the presenter sees the name of the device and accepts or declines. Only then do audience window and presenter view contact the phone, and it builds a direct connection to each of them.

Image and sound go from device to device (WebRTC, encrypted). Only the brokering runs via the platform's server: who requests, who accepts, how the devices reach each other. There is no table for it and no recording.

Every movement is a command at the core of the editor — pairing, accepting, sound, volume, mirroring, full screen, disconnecting —, whether by button, voice, gesture or from a second window. That is why audience window and presenter view always show the same state.

Data protection#

  • On the phone a consent notice appears before the first image: what is sent, where to, and that nothing is stored.
  • Nothing is recorded — neither on the phone nor in the presentation nor on the server. A guard in the code ensures this.
  • If the presentation records itself (video export), the live source stays as the placeholder.
  • Only the presenter sees the QR code (in the presentation only after a click); every device must be accepted and can be disconnected at any time — from both sides.
  • A routing server (STUN) only learns the public address of the devices; a relay server (TURN), if set up, passes on the encrypted stream without being able to read it.

Limits#

  • Without a relay server (TURN) some networks fail (university Wi-Fi with device isolation, mobile networks). What helps then: put both devices on the same Wi-Fi.
  • Screen sharing only on a computer; not in the browser on phones and tablets.
  • The sound only plays in the audience window; without an open audience window the sound is muted. If the browser only allows sound after a click, “Turn on sound” appears on the source.
  • PPTX and PDF export show a named spot instead of the live image; the course player shows the placeholder.
  • Voice commands understand German and English.

Tips#

  • Several phones: one per live source. The same identifier (q1, q2 …) on several slides is the same source — it stays connected when the slide changes.
  • The sound only plays in the audience window. The presenter view and the editor show the image muted — otherwise there would be echo. Microphone and loudspeaker in the same room: keep the volume moderate, keep your distance.
  • Voice: “connect phone”, “mute”, “unmute”, “louder”, “quieter”, “full screen”, “full screen off” / “back to slide”, “mirror”, “disconnect phone”; with number or label (“source 2 full screen”, “board mute”) — in English and German.
  • Gestures (camera gestures in the console): hand up = full screen, down = back to slide, swipe = next connected source in full screen, fist = mute, open hand = unmute.
  • Screen sharing works in the browser on a computer (e.g. to include a second laptop). On phones and tablets the browser cannot share a screen — that comes with the apps. Photo or video from the phone works everywhere.
  • If the code has expired (after 15 minutes without a request), simply pair again. A phone that is already connected stays connected.

Related features#