How We Keep Your Binge Call in Sync Under 50ms

Two Problems, Two Transports

BingeCall needs to solve two different synchronization problems:

Video sync — when you press play, everyone else needs to see play within ~50ms

Presence — knowing who's in the room, their names, video chat status

These have different latency requirements, so we use different transports for each.

Socket.io for Video Sync

For video sync events (play, pause, seek, heartbeat), we use a stateless Socket.io server. When you press play:

Your extension emits `sync:action` to the signaling server

The server broadcasts it to everyone else in the room

Each client applies the action — but only if the `isSyncAction` flag isn't already set

The `isSyncAction` flag is the anti-echo pattern. Without it, when you receive a "play" command and apply it, the video's `play` event fires — which would re-broadcast to everyone, creating an infinite loop.

Drift Correction via Heartbeat

Every 3 seconds, the host sends a heartbeat with the current video timestamp. Receivers compare it to their local position:

Within 1 second: soft resync (no seek, just let it drift back naturally)

More than 5 seconds: hard resync (seek immediately)

This handles cases where someone's stream buffers and falls behind without any explicit "pause to buffer" event.

Supabase Realtime for Presence

For presence (who's in the room), we use Supabase Realtime channels. The ~150ms latency here is acceptable — you don't need sub-50ms updates to know that someone joined the party.

Using Supabase for this also means the extension gets presence updates even if the Socket.io connection momentarily drops, since they're on separate transports.

WebRTC for Video Calls

Video calls use P2P WebRTC with a mesh topology (everyone connects to everyone). For rooms up to 6 people, this is simpler and lower latency than a media server. For larger rooms, we'd need to switch to an SFU — but that's a future problem.

TURN credentials are generated on-demand by an Edge Function using HMAC-SHA1, valid for 1 hour. They're never stored.