Medium, method and system for ad hoc, ambient, synchronous multimedia collaboration in a group-based communication system. Embodiments of the invention provide a way for users to quickly establish a real-time collaboration among a group of peers without the burden and overhead of a conventional call or video meeting. Users can quickly and easily join and leave these synchronous multimedia collaboration sessions at any time, without disrupting the session for other users. This enables the user to experience the collaboration as a convenient forum rather than a burdensome scheduled event.