KoalaSync

KoalaSync is a free and open-source browser extension for watching videos together online.

The idea is simple: create a room, share an invite link, and KoalaSync keeps video playback in sync between everyone in that room. It synchronizes play, pause, seeking, and episode changes, so you do not have to keep doing the usual “3, 2, 1, play” countdown over Discord or a voice call.

I originally built it for my own self-hosted Emby setup, because I wanted to watch movies and shows with friends without manually re-syncing every pause or episode change. Since then it has grown into a more general watch party extension for browser-based video players.

It works with many HTML5/browser video players, including self-hosted media servers like Emby, Jellyfin, and Plex, as well as platforms like YouTube, Netflix, Disney+, Prime Video, Twitch and more. It can even sync local video files opened directly in the browser.

KoalaSync does not require accounts, emails, subscriptions, or tracking. Rooms are temporary, the public relay server only coordinates synchronization state, and advanced users can also self-host their own relay server with Docker.

Some current features:

• real-time play/pause/seek synchronization
• room invite links
• support for many browser-based video players
• self-hosted media server support
• optional self-hosted relay server
• no account required
• no tracking
• 13 interface languages
• local audio compressor for quiet dialogue and loud action scenes
• lazy connection handling, so the extension only connects when it is actually being used

KoalaSync is mainly useful for remote movie nights, long-distance couples, friends watching shows together, and self-hosted media users who want a lightweight alternative to platform-specific watch party tools.