Virtual Classroom on a Slow Internet Connection

A live class is three streams at once: the teacher's camera, their screen share and everyone's audio. On a connection that dips below roughly 1 Mbps upstream, the browser has to choose what to drop. Left alone it drops the wrong thing — usually audio continuity — and the lesson becomes unfollowable even though video keeps updating.

This classroom runs LiveKit with adaptive stream and dynacast enabled. Adaptive stream means each viewer only receives the resolution their tile actually needs, so a student watching on a phone never pulls a 1080p layer. Dynacast stops publishing layers nobody is subscribed to, which frees the teacher's upstream bandwidth for the screen share that matters.

Simulcast sits underneath both: the publisher sends several quality layers, and the server hands each subscriber the highest one their measured bandwidth can sustain. Recovery is automatic — when the connection improves the layer steps back up without a reconnect.

Students can override the automatic choice with the quality selector in the class footer. Picking 480p instead of Auto tells the server to stop offering higher layers at all, which is better than letting the connection oscillate between 720p and a stall. On a metered mobile plan this also cuts data use substantially.

Rooms publish VP8 rather than VP9 or AV1. It is not the most efficient codec, but it is hardware-decoded almost everywhere — older Android phones, Safari on aging iPads, Firefox — so a weak device spends its budget on the network instead of on software decoding. A stream that decodes in hardware drops far fewer frames on a poor link.

If you have to choose, keep audio. Turning off the student camera removes an upstream video track entirely and often stabilises a class outright. Teachers presenting slides can also switch the student view to screen-only with the presenter toggle, which suppresses the camera track for everyone and roughly halves what each viewer downloads.

• Have them cap quality to 480p rather than leaving it on Auto.
• Turn their camera off; a publishing track competes with what they receive.
• Switch from Wi-Fi to wired, or move closer to the access point.
• Close other tabs — a background video eats the same downstream budget.
• Watch the reconnecting banner: if it appears repeatedly, the problem is packet loss, not bandwidth, and a network change is the only real fix.

Share a specific window rather than the whole desktop, avoid full-screen video inside a share (screen-share encoding assumes mostly-static content), and prefer larger text over higher resolution. A 720p share of large type reads better on a phone than a 1080p share of small type at half the frame rate.